Display device including two display elements, display module, electronic device, and method for manufacturing display device

ABSTRACT

A first display element includes a first pixel electrode that reflects visible light, a liquid crystal layer, and a first common electrode that transmits visible light. A second display element includes a second pixel electrode that transmits visible light, a light-emitting layer, and a second common electrode that reflects visible light. A separation layer that reflects visible light is formed over a formation substrate, an insulating layer is formed over the separation layer, and the second display element is formed over the insulating layer. The formation substrate and a second substrate are bonded to each other. Then, the formation substrate and the separation layer are separated from each other. The exposed separation layer is processed into the first pixel electrode. The liquid crystal layer is positioned between the first common electrode and the first pixel electrode and a first substrate and the second substrate are bonded to each other.

BACKGROUND OF THE INVENTION 1. Field of the Invention

One embodiment of the present invention relates to a display device, a display module, an electronic device, and a manufacturing method of a display device.

Note that one embodiment of the present invention is not limited to the above technical field. Examples of the technical field of one embodiment of the present invention include a semiconductor device, a display device, a light-emitting device, a power storage device, a memory device, an electronic device, a lighting device, an input device (such as a touch sensor), an input/output device (such as a touch panel), a driving method thereof, and a manufacturing method thereof.

2. Description of the Related Art

Recent display devices have been expected to be applied to a variety of uses. Light-emitting devices including light-emitting elements, liquid crystal display devices including liquid crystal elements, and the like have been developed as display devices.

Patent Document 1, for example, discloses a flexible light-emitting device to which an organic electroluminescent (EL) element is applied.

Patent Document 2 discloses a transflective liquid crystal display device having a region reflecting visible light and a region transmitting visible light. The transflective liquid crystal display device can be used as a reflective liquid crystal display device in an environment where sufficient external light can be obtained and as a transmissive liquid crystal display device in an environment where sufficient external light cannot be obtained.

REFERENCE Patent Documents

-   [Patent Document 1] Japanese Published Patent Application No.     2014-197522 -   [Patent Document 2] Japanese Published Patent Application No.     2011-191750

SUMMARY OF THE INVENTION

An object of one embodiment of the present invention is to provide a display device with low power consumption. Another object of one embodiment of the present invention is to provide a display device with high visibility regardless of the ambient brightness. Another object of one embodiment of the present invention is to provide an all-weather display device. Another object of one embodiment of the present invention is to provide a display device with high convenience. Another object of one embodiment of the present invention is to reduce the thickness or weight of a display device. Another object of one embodiment of the present invention is to provide a novel display device, a novel input/output device, a novel electronic device, or the like.

Another object of one embodiment of the present invention is to provide a method for manufacturing a novel display device. Another object of one embodiment of the present invention is to provide a method for manufacturing a display device with a simplified manufacturing process. Another object of one embodiment of the present invention is to provide a method for manufacturing a display device with high mass productivity at low cost.

Note that the descriptions of these objects do not preclude the existence of other objects. One embodiment of the present invention does not necessarily achieve all the objects. Other objects can be derived from the description of the specification, the drawings, and the claims.

A display device of one embodiment of the present invention includes a first display element, a second display element, and an insulating layer. The first display element includes a first pixel electrode configured to reflect visible light and a liquid crystal layer. The second display element is configured to emit visible light. The second display element includes a second pixel electrode and a common electrode. The first pixel electrode is positioned on an opposite side of the insulating layer from the second pixel electrode. The liquid crystal layer is positioned on an opposite side of the first pixel electrode from the insulating layer. The common electrode is positioned on an opposite side of the second pixel electrode from the insulating layer. The liquid crystal layer includes a first region overlapping with the first pixel electrode and a second region overlapping with the second display element. A thickness of the liquid crystal layer in the first region is smaller than a thickness of the liquid crystal layer in the second region. The display device preferably includes a first transistor and a second transistor. The first transistor is configured to control driving of the first display element. The second transistor is configured to control driving of the second display element. The insulating layer includes a portion serving as a gate insulating layer of the first transistor and a portion serving as a gate insulating layer of the second transistor.

A display device of one embodiment of the present invention includes a first display element, a second display element, a first insulating layer, a second insulating layer, a first transistor, and a second transistor. The first transistor is configured to control driving of the first display element. The second transistor is configured to control driving of the second display element. The first display element includes a first pixel electrode configured to reflect visible light and a liquid crystal layer. The second display element is configured to emit visible light. The second display element includes a second pixel electrode and a common electrode. The first transistor and the second transistor are positioned between the first insulating layer and the second insulating layer. The first transistor is electrically connected to the first pixel electrode through an opening in the first insulating layer. The second transistor is electrically connected to the second pixel electrode through an opening in the second insulating layer. The liquid crystal layer is positioned on an opposite side of the first pixel electrode from the first insulating layer. The common electrode is positioned on an opposite side of the second pixel electrode from the second insulating layer. The liquid crystal layer includes a first region overlapping with the first pixel electrode and a second region overlapping with the second display element. A thickness of the liquid crystal layer in the first region is smaller than a thickness of the liquid crystal layer in the second region.

One or both of the first transistor and the second transistor preferably include an oxide semiconductor in a channel formation region.

The first pixel electrode may include an opening portion. The second display element includes a region overlapping with the opening portion. The second display element is configured to emit visible light toward the opening portion.

One embodiment of the present invention is a display module including any of the above display devices and a circuit board such as a flexible printed circuit (FPC).

One embodiment of the present invention is an electronic device including the above display module and at least one of an antenna, a battery, a housing, a camera, a speaker, a microphone, and an operation button.

One embodiment of the present invention is a method for manufacturing a display device including a first display element, a second display element, and an insulating layer. The first display element includes a first pixel electrode configured to reflect visible light, a liquid crystal layer, and a first common electrode configured to transmit visible light. The second display element includes a second pixel electrode configured to transmit visible light, a light-emitting layer, and a second common electrode configured to reflect visible light. The first common electrode is formed over a first substrate, a separation layer configured to reflect visible light is formed over a formation substrate, and the insulating layer is formed over the separation layer. The second pixel electrode, the light-emitting layer, and the second common electrode are formed in this order over the insulating layer to form the second display element. The formation substrate and a second substrate are bonded to each other with an adhesive. The formation substrate and the separation layer are separated from each other. The exposed separation layer is processed into the first pixel electrode. The liquid crystal layer is positioned between the first common electrode and the first pixel electrode, and the first substrate and the second substrate are bonded to each other with an adhesive to form the first display element.

In the above method for manufacturing a display device, the separation layer may be processed into the first pixel electrode having an opening in a region overlapping with the second display element.

In the above method for manufacturing a display device, the adhesive used for bonding the first substrate and the second substrate to each other preferably contains a conductive particle. The separation layer may be processed into the first pixel electrode and a conductive layer. The first common electrode and the conductive layer may be electrically connected to each other via the conductive particle when the first substrate and the second substrate are bonded to each other.

One embodiment of the present invention is a method for manufacturing a display device including a first display element, a second display element, and an insulating layer. The first display element includes a first pixel electrode configured to reflect visible light, a liquid crystal layer, and a first common electrode configured to transmit visible light. The second display element includes a second pixel electrode configured to transmit visible light, a light-emitting layer, and a second common electrode configured to reflect visible light. The first common electrode is formed over a first substrate, a separation layer is formed over a formation substrate, the first pixel electrode is formed over the separation layer, and the insulating layer is formed over the first pixel electrode. The second pixel electrode, the light-emitting layer, and the second common electrode are formed in this order over the insulating layer to form the second display element. The formation substrate and a second substrate are bonded to each other with an adhesive. The formation substrate and the separation layer are separated from each other. The exposed separation layer is removed so that the insulating layer and the first pixel electrode are exposed. The liquid crystal layer is positioned between the first common electrode and the first pixel electrode, and the first substrate and the second substrate are bonded to each other with an adhesive to form the first display element.

In the above method for manufacturing a display device, after the first pixel electrode is formed, an opening may be provided in the first pixel electrode and the second display element may be formed in a region overlapping with the opening.

In the above method for manufacturing a display device, the adhesive used for bonding the first substrate and the second substrate to each other preferably contains a conductive particle. A conductive film may be processed into the first pixel electrode and a conductive layer. The first common electrode and the conductive layer may be electrically connected to each other via the conductive particle when the first substrate and the second substrate are bonded to each other.

In any of the above methods for manufacturing a display device, a nickel film may be formed as the separation layer in contact with the formation substrate. The maximum temperature applied to the separation layer in a period from forming the separation layer until separating the formation substrate and the separation layer from each other is preferably higher than 150° C. and lower than 450° C.

In any of the above methods for manufacturing a display device, a first insulating layer containing nitrogen and silicon may be formed over the formation substrate, a second insulating layer containing oxygen and silicon may be formed over the first insulating layer, a third insulating layer containing oxygen, fluorine, and silicon may be formed over the second insulating layer, and a titanium film may be formed as the separation layer over the third insulating layer.

According to one embodiment of the present invention, a display device with low power consumption can be provided. According to one embodiment of the present invention, a display device with high visibility regardless of the ambient brightness can be provided. According to one embodiment of the present invention, an all-weather display device can be provided. According to one embodiment of the present invention, a display device with high convenience can be provided. According to one embodiment of the present invention, the thickness or weight of a display device can be reduced. According to one embodiment of the present invention, a novel display device, a novel input/output device, a novel electronic device, or the like can be provided.

According to one embodiment of the present invention, a method for manufacturing a novel display device can be provided. According to one embodiment of the present invention, a method for manufacturing a display device with a simplified manufacturing process can be provided. According to one embodiment of the present invention, a method for manufacturing a display device with high mass productivity at low cost can be provided.

Note that the descriptions of these effects do not preclude the existence of other effects. One embodiment of the present invention does not necessarily have all the effects. Other effects can be derived from the description of the specification, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating an example of a display device.

FIG. 2 is a cross-sectional view illustrating an example of a display device.

FIG. 3 is a cross-sectional view illustrating an example of a display device.

FIGS. 4A and 4B are cross-sectional views each illustrating an example of a display device.

FIGS. 5A, 5B1, 5B2, and 5C are cross-sectional views illustrating an example of a manufacturing method of a display device.

FIGS. 6A to 6C are cross-sectional views illustrating an example of a manufacturing method of a display device.

FIGS. 7A to 7C are cross-sectional views illustrating an example of a manufacturing method of a display device.

FIGS. 8A and 8B are cross-sectional views illustrating an example of a manufacturing method of a display device.

FIGS. 9A, 9B, 9C1, and 9C2 are cross-sectional views each illustrating an example of a manufacturing method of a display device.

FIGS. 10A and 10B are cross-sectional views illustrating an example of a manufacturing method of a display device.

FIGS. 11A and 11B are cross-sectional views illustrating an example of a manufacturing method of a display device.

FIGS. 12A and 12B are cross-sectional views illustrating an example of a manufacturing method of a display device.

FIGS. 13A and 13B are cross-sectional views each illustrating an example of a manufacturing method of a display device.

FIGS. 14A to 14E are cross-sectional views illustrating examples of transistors.

FIG. 15A illustrates an example of a display device, and FIGS. 15B1, 15B2, 15B3, and 15B4 each illustrate an example of a pixel.

FIG. 16 is a circuit diagram illustrating an example of a pixel circuit in a display device.

FIG. 17A is a circuit diagram illustrating an example of a pixel circuit in a display device, and FIG. 17B is a diagram illustrating an example of a pixel.

FIG. 18 illustrates an example of a display module.

FIGS. 19A to 19D illustrate examples of electronic devices.

FIGS. 20A to 20E illustrate examples of electronic devices.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be described in detail with reference to drawings. Note that the present invention is not limited to the following description, and it is easily understood by those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. Accordingly, the present invention should not be interpreted as being limited to the description of the embodiments below.

Note that in the structures of the invention described below, the same portions or portions having similar functions are denoted by the same reference numerals in different drawings, and description of such portions is not repeated. Further, the same hatching pattern is applied to portions having similar functions, and the portions are not denoted by reference numerals in some cases.

The position, size, range, or the like of each structure illustrated in drawings is not accurately represented in some cases for easy understanding. Therefore, the disclosed invention is not necessarily limited to the position, size, range, or the like disclosed in the drawings.

Note that the terms “film” and “layer” can be interchanged with each other depending on the case or circumstances. For example, the term “conductive layer” can be changed into the term “conductive film,” and the term “insulating film” can be changed into the term “insulating layer.”

In this specification and the like, a metal oxide means an oxide of metal in a broad sense. Metal oxides are classified into an oxide insulator, an oxide conductor (including a transparent oxide conductor), an oxide semiconductor (also simply referred to as an OS), and the like. For example, a metal oxide used in a semiconductor layer of a transistor is called an oxide semiconductor in some cases. In other words, an OS FET is a transistor including a metal oxide or an oxide semiconductor.

In this specification and the like, a metal oxide including nitrogen is also called a metal oxide in some cases. Moreover, a metal oxide including nitrogen may be called a metal oxynitride.

In this specification and the like, “c-axis aligned crystal (CAAC)” or “cloud-aligned composite (CAC)” might be stated. CAAC refers to an example of a crystal structure, and CAC refers to an example of a function or a material composition.

An example of a crystal structure of an oxide semiconductor or a metal oxide is described. Note that an oxide semiconductor deposited by a sputtering method using an In—Ga—Zn oxide target (In:Ga:Zn=4:2:4.1 in an atomic ratio) is described below as an example. An oxide semiconductor formed by a sputtering method using the above-mentioned target at a substrate temperature of higher than or equal to 100° C. and lower than or equal to 130° C. is referred to as sIGZO, and an oxide semiconductor formed by a sputtering method using the above-mentioned target with the substrate temperature set at room temperature (R.T.) is referred to as tIGZO. For example, sIGZO has one or both crystal structures of nano crystal (nc) and CAAC. Furthermore, tIGZO has a crystal structure of nc. Note that room temperature (R.T.) herein also refers to a temperature of the time when a substrate is not heated intentionally.

In this specification and the like, CAC-OS or CAC-metal oxide has a function of a conductor in a part of the material and has a function of a dielectric (or insulator) in another part of the material; as a whole, CAC-OS or CAC-metal oxide has a function of a semiconductor. In the case where CAC-OS or CAC-metal oxide is used in a semiconductor layer of a transistor, the conductor has a function of letting electrons (or holes) serving as carriers flow, and the dielectric has a function of not letting electrons serving as carriers flow. By the complementary action of the function as a conductor and the function as a dielectric, CAC-OS or CAC-metal oxide can have a switching function (on/off function). In the CAC-OS or CAC-metal oxide, separation of the functions can maximize each function.

In this specification and the like, CAC-OS or CAC-metal oxide includes conductor regions and dielectric regions. The conductor regions have the above-described function of the conductor, and the dielectric regions have the above-described function of the dielectric. In some cases, the conductor regions and the dielectric regions in the material are separated at the nanoparticle level. In some cases, the conductor regions and the dielectric regions are unevenly distributed in the material. When observed, the conductor regions are coupled in a cloud-like manner with their boundaries blurred, in some cases.

In other words, CAC-OS or CAC-metal oxide can be called a matrix composite or a metal matrix composite.

Furthermore, in the CAC-OS or CAC-metal oxide, the conductor regions and the dielectric regions each have a size of more than or equal to 0.5 nm and less than or equal to 10 nm, preferably more than or equal to 0.5 nm and less than or equal to 3 nm and are dispersed in the material, in some cases.

Embodiment 1

In this embodiment, a display device of one embodiment of the present invention and a method for manufacturing the display device will be described with reference to drawings.

The display device of this embodiment includes a first display element reflecting visible light and a second display element emitting visible light.

The display device of this embodiment has a function of displaying an image using one or both of light reflected by the first display element and light emitted from the second display element.

As the first display element, an element which displays an image by reflecting external light can be used. Such an element does not include a light source (or does not require an artificial light source); thus, power consumed in displaying an image can be significantly reduced.

As a typical example of the first display element, a reflective liquid crystal element can be given. As the first display element, an element using a microcapsule method, an electrophoretic method, an electrowetting method, an Electronic Liquid Powder (registered trademark) method, or the like can also be used, other than Micro Electro Mechanical Systems (MEMS) shutter element or an optical interference type MEMS element.

As the second display element, a light-emitting element is preferably used. Since the luminance and the chromaticity of light emitted from the light-emitting element are not affected by external light, a clear image that has high color reproducibility (wide color gamut) and a high contrast can be displayed.

As the second display element, a self-luminous light-emitting element such as an organic light-emitting diode (OLED), a light-emitting diode (LED), a quantum-dot light-emitting diode (QLED), or a semiconductor laser can be used.

The display device of this embodiment has a first mode in which an image is displayed using only the first display element, a second mode in which an image is displayed using only the second display element, and a third mode in which an image is displayed using both the first display element and the second display element. The display device of this embodiment can be switched between these modes automatically or manually.

In the first mode, an image is displayed using the first display element and external light. Because a light source is unnecessary in the first mode, power consumed in this mode is extremely low. When sufficient external light enters the display device (e.g., in a bright environment), for example, an image can be displayed by using light reflected by the first display element. The first mode is effective in the case where external light is white light or light near white light and is sufficiently strong, for example. The first mode is suitably used for displaying text. Furthermore, the first mode enables eye-friendly display owing to the use of reflected external light, which leads to an effect of easing eyestrain.

In the second mode, an image is displayed using light emitted from the second display element. Thus, an extremely vivid image (with high contrast and excellent color reproducibility) can be displayed regardless of the illuminance and the chromaticity of external light. The second mode is effective in the case of extremely low illuminance, such as in a night environment or in a dark room, for example. When a bright image is displayed in a dark environment, a user may feel that the image is too bright. To prevent this, an image with reduced luminance is preferably displayed in the second mode. In that case, glare can be reduced, and power consumption can also be reduced. The second mode is suitably used for displaying a vivid (still and moving) image or the like.

In the third mode, an image is displayed using both light reflected by the first display element and light emitted from the second display element. An image displayed in the third mode can be more vivid than an image displayed in the first mode while power consumption can be lower than that in the second mode. The third mode is effective in the case where the illuminance is relatively low or in the case where the chromaticity of external light is not white, for example, in an environment under indoor illumination or in the morning or evening.

With such a structure, an all-weather display device or a highly convenient display device with high visibility regardless of the ambient brightness can be fabricated.

The display device of this embodiment includes a plurality of first pixels including first display elements and a plurality of second pixels including second display elements. The first pixels and the second pixels are preferably arranged in matrices.

Each of the first pixels and the second pixels can include one or more sub-pixels. For example, each pixel can include one sub-pixel (e.g., a white (W) sub-pixel), three sub-pixels (e.g., red (R), green (G), and blue (B) sub-pixels, or yellow (Y), cyan (C), and magenta (M) sub-pixels), or four sub-pixels (e.g., red (R), green (G), blue (B), and white (W) sub-pixels, or red (R), green (G), blue (B), and yellow (Y) sub-pixels).

The display device of this embodiment can display a full-color image using either the first pixels or the second pixels. Alternatively, the display device of this embodiment can display a black-and-white image or a grayscale image using the first pixels and can display a full-color image using the second pixels. The first pixels that can be used for displaying a black-and-white image or a grayscale image are suitable for displaying information that need not be displayed in color such as text information.

Next, structure examples of the display device of this embodiment will be described with reference to FIG. 1, FIG. 2, FIG. 3, and FIGS. 4A and 4B.

Structure Example 1

FIG. 1 is a schematic perspective view of a display device 300. In the display device 300, a substrate 351 and a substrate 361 are bonded to each other. In FIG. 1, the substrate 361 is denoted by dashed lines.

The display device 300 includes a display portion 362, a circuit 364, a wiring 365, and the like. FIG. 1 illustrates an example in which the display device 300 is provided with an integrated circuit (IC) 373 and an FPC 372. Thus, the structure illustrated in FIG. 1 can be regarded as a display module including the display device 300, the IC, and the FPC.

As the circuit 364, for example, a scan line driver circuit can be used.

The wiring 365 has a function of supplying a signal and power to the display portion 362 and the circuit 364. The signal and power are input to the wiring 365 from the outside through the FPC 372 or from the IC 373.

FIG. 1 illustrates an example in which the IC 373 is provided over the substrate 351 by a chip on glass (COG) method, a chip on film (COF) method, or the like. An IC including a scan line driver circuit, a signal line driver circuit, or the like can be used as the IC 373, for example. Note that the display device 300 and the display module are not necessarily provided with an IC. The IC may be mounted on the FPC by a COF method or the like.

FIG. 1 illustrates an enlarged view of part of the display portion 362. Electrodes 311 a included in a plurality of display elements are arranged in a matrix in the display portion 362. The electrodes 311 a each have a function of reflecting visible light, and serve as a reflective electrode of a liquid crystal element 180.

The method for manufacturing the display device of this embodiment includes a separation step in which a transistor, a display element, and the like formed over a formation substrate are peeled from the formation substrate.

In the separation step, the peeling is performed between the formation substrate and a separation layer.

In this embodiment, a conductive layer having a function of reflecting visible light is used as the separation layer. The separation layer is processed into a conductive layer in the display device after being exposed by the peeling. Specifically, the electrode 311 a serving as a reflective electrode of the liquid crystal element 180 can be formed using the separation layer.

In the case of forming the electrode 311 a using the separation layer, the removal of the separation layer is not required. In addition, a conductive film to be the electrode 311 a does not need to be formed in a different step than the separation layer. Accordingly, a manufacturing process can be simplified.

Examples of a material for the separation layer (i.e., a material for the electrode 311 a) include nickel (Ni), titanium (Ti), and silver (Ag), and an alloy containing any of these elements. As an alloy containing silver, for example, an alloy of silver and copper, an alloy of silver, palladium, and copper (also referred to as Ag—Pd—Cu or APC), or an alloy of silver and magnesium can be given.

The separation layer may be formed in contact with the formation substrate. In that case, separation occurs in the separation step at the interface between the formation substrate and the separation layer. When the separation layer is formed in contact with a glass substrate, the layer hardly remains on the formation substrate after the peeling, leading to easy reuse of the formation substrate.

It is preferable to form a nickel film in contact with the glass substrate, for example. In that case, separation can occur in the separation step at the interface between the glass substrate and the nickel film.

The separation layer may be formed over the formation substrate with an insulating layer including one or more layers provided therebetween. In that case, separation occurs in the separation step at the interface between the separation layer and an insulating layer in contact with the separation layer.

It is preferable to form, for example, an insulating layer over the formation substrate and a titanium film in contact with the insulating layer. In that case, separation can occur in the separation step at the interface between the insulating layer and the titanium film. Titanium is preferably used for the separation layer because of its low price and easy application to large substrates.

The electrode 311 a is preferably formed using a separation layer containing silver, in which case the visible light reflectance can be increased.

When the separation layer contains nickel, titanium, or the like, a surface of the separation layer does not particularly need to be subjected to treatment such as plasma treatment. Thus, the display device can be manufactured through fewer steps at lower cost.

As described above, the display device of this embodiment can be manufactured with high mass productivity at low cost. The details of the method for manufacturing the display device will be described later.

As illustrated in FIG. 1, the electrode 311 a includes an opening 451. In addition, the display portion 362 includes a light-emitting element 170 that is positioned closer to the substrate 351 than the electrode 311 a. Light from the light-emitting element 170 is emitted to the substrate 361 side through the opening 451 in the electrode 311 a. The area of the light-emitting region of the light-emitting element 170 may be equal to the area of the opening 451. One of the area of the light-emitting region of the light-emitting element 170 and the area of the opening 451 is preferably larger than the other because a margin for misalignment can be increased. It is particularly preferable that the area of the opening 451 be larger than the area of the light-emitting region of the light-emitting element 170. When the area of the opening 451 is small, part of light from the light-emitting element 170 is blocked by the electrode 311 a and cannot be extracted to the outside, in some cases. The opening 451 with a sufficiently large area can reduce waste of light emitted from the light-emitting element 170.

FIG. 2 illustrates an example of cross-sections of part of a region including the FPC 372, part of a region including the circuit 364, and part of a region including the display portion 362 of the display device 300 illustrated in FIG. 1.

The display device 300 illustrated in FIG. 2 includes a transistor 201, a transistor 203, a transistor 205, a transistor 206, the liquid crystal element 180, the light-emitting element 170, an insulating layer 220, a coloring layer 131, a coloring layer 134, and the like, between the substrate 351 and the substrate 361. The substrate 361 and the insulating layer 220 are bonded to each other with an adhesive layer 141. The substrate 351 and the insulating layer 220 are bonded to each other with the adhesive layer 142.

The substrate 361 is provided with the coloring layer 131, a light-blocking layer 132, an insulating layer 121, an electrode 113 functioning as a common electrode of the liquid crystal element 180, an alignment film 133 b, an insulating layer 117, and the like. A polarizing plate 135 is provided on an outer surface of the substrate 361. The insulating layer 121 may have a function of a planarization layer. The insulating layer 121 enables the electrode 113 to have an almost flat surface, resulting in a uniform alignment state of a liquid crystal layer 112. The insulating layer 117 serves as a spacer for holding a cell gap of the liquid crystal element 180. In the case where the insulating layer 117 transmits visible light, the insulating layer 117 may be positioned to overlap with a display region of the liquid crystal element 180.

The liquid crystal element 180 is a reflective liquid crystal element. The liquid crystal element 180 reflects light to the substrate 361 side. The liquid crystal element 180 has a stacked-layer structure of the electrode 311 a, the liquid crystal layer 112, and the electrode 113. The electrode 311 a functions as a pixel electrode. The electrode 311 a includes the opening 451. The electrode 113 functions as the common electrode. An alignment film 133 a is provided between the liquid crystal layer 112 and the electrode 311 a. The alignment film 133 b is provided between the liquid crystal layer 112 and the electrode 113.

In the liquid crystal element 180, the electrode 311 a has a function of reflecting visible light, and the electrode 113 has a function of transmitting visible light. Light entering from the substrate 361 side is polarized by the polarizing plate 135, transmitted through the electrode 113 and the liquid crystal layer 112, and reflected by the electrode 311 a. Then, the light is transmitted through the liquid crystal layer 112 and the electrode 113 again to reach the polarizing plate 135. In this case, alignment of a liquid crystal can be controlled with a voltage that is applied between the electrode 311 a and the electrode 113, and thus optical modulation of light can be controlled. In other words, the intensity of light emitted through the polarizing plate 135 can be controlled. Light excluding light in a particular wavelength region is absorbed by the coloring layer 131, and thus, emitted light is red light, for example.

The thickness of the liquid crystal layer 112 differs in a portion where the electrode 311 a is provided and in a portion where the electrode 311 a is not provided. Specifically, in the liquid crystal layer 112, a thickness T1 of the portion where the electrode 311 a is provided is smaller than a thickness T2 of the portion where the electrode 311 a is not provided.

At a connection portion 207, the electrode 311 a is electrically connected to a conductive layer 222 a included in the transistor 206 via a conductive layer 221 b. The transistor 206 has a function of controlling the driving of the liquid crystal element 180.

A connection portion 252 is provided in part of a region where the adhesive layer 141 is provided. At the connection portion 252, a conductive layer 311 c is electrically connected to part of the electrode 113 through a connector 243. The electrode 311 a and the conductive layer 311 c can be formed by processing the same conductive film. Accordingly, a signal or a potential input from the FPC 372 connected to the substrate 351 side can be supplied to the electrode 113 formed on the substrate 361 side through the connection portion 252.

As the connector 243, for example, a conductive particle can be used. As the conductive particle, a particle of an organic resin, silica, or the like coated with a metal material can be used. It is preferable to use nickel or gold as the metal material because contact resistance can be decreased. It is also preferable to use a particle coated with layers of two or more kinds of metal materials, such as a particle coated with nickel and further with gold. A material capable of elastic deformation or plastic deformation is preferably used for the connector 243. As illustrated in FIG. 2, the connector 243, which is the conductive particle, has a shape that is vertically crushed in some cases. With the crushed shape, the contact area between the connector 243 and a conductive layer electrically connected to the connector 243 can be increased, thereby reducing contact resistance and suppressing the generation of problems such as disconnection.

The connector 243 is preferably provided so as to be covered with the adhesive layer 141. For example, the connectors 243 can be dispersed in the adhesive layer 141 before curing of the adhesive layer 141.

The light-emitting element 170 is a bottom-emission light-emitting element. The light-emitting element 170 has a stacked-layer structure in which an electrode 191, an EL layer 192, and an electrode 193 are stacked in this order from the insulating layer 220 side. The electrode 191 functions as a pixel electrode. The EL layer 192 contains at least a light-emitting substance. The electrode 193 functions as a common electrode. The light-emitting element 170 is an electroluminescent element that emits light to the substrate 361 side when voltage is applied between the electrode 191 and the electrode 193.

The electrode 191 is connected to the conductive layer 222 a included in the transistor 205 through an opening provided in an insulating layer 212, an insulating layer 213, and an insulating layer 214. The transistor 205 has a function of controlling the driving of the light-emitting element 170. An insulating layer 216 covers an end portion of the electrode 191.

The electrode 191 has a function of transmitting visible light. The electrode 193 preferably has a function of reflecting visible light.

The light-emitting element 170 is preferably covered with an insulating layer 194. In FIG. 2, the insulating layer 194 is provided in contact with the electrode 193. The insulating layer 194 can prevent an impurity from entering the light-emitting element 170, leading to an increase in the reliability of the light-emitting element 170. The insulating layer 194 and the substrate 351 are bonded to each other with an adhesive layer 142.

Light is emitted from the light-emitting element 170 to the substrate 361 side through the coloring layer 134, the insulating layer 220, the opening 451, and the like.

The liquid crystal element 180 and the light-emitting element 170 can exhibit various colors when the color of the coloring layer varies among pixels. The display device 300 can display a color image using the liquid crystal element 180. The display device 300 can display a color image using the light-emitting element 170.

The transistor 201, the transistor 203, the transistor 205, and the transistor 206 are formed on a plane of the insulating layer 220 on the substrate 351 side. These transistors can be fabricated through the same process.

A circuit electrically connected to the liquid crystal element 180 and a circuit electrically connected to the light-emitting element 170 are preferably formed on the same plane. In that case, the thickness of the display device can be smaller than that in the case where the two circuits are formed on different planes. Furthermore, since two transistors can be formed in the same process, a manufacturing process can be simplified as compared to the case where two transistors are formed on different planes.

The electrode 311 a, which serves as the pixel electrode of the liquid crystal element 180, is positioned on the opposite side of a gate insulating layer (an insulating layer 211) included in the transistors from the electrode 191, which serves as the pixel electrode of the light-emitting element 170.

In the case where a transistor including an oxide semiconductor in its channel formation region and having extremely low off-state current is used as the transistor 206 or in the case where a memory element electrically connected to the transistor 206 is used, for example, in displaying a still image using the liquid crystal element 180, even if writing operation to a pixel is stopped, the gray level can be maintained. In other words, an image can be kept displayed even with an extremely low frame rate. In one embodiment of the present invention, the frame rate can be extremely low and driving with low power consumption can be performed.

The transistor 203 is used for controlling whether the pixel is selected or not (such a transistor is also referred to as a switching transistor or a selection transistor). The transistor 205 is used for controlling current flowing to the light-emitting element 170 (such a transistor is also referred to as a driving transistor).

Insulating layers such as the insulating layer 211, the insulating layer 212, the insulating layer 213, and the insulating layer 214 are provided on the substrate 351 side of the insulating layer 220. Part of the insulating layer 211 functions as a gate insulating layer of each transistor. The insulating layer 212 is provided to cover the transistor 206 and the like. The insulating layer 213 is provided to cover the transistor 205 and the like. The insulating layer 214 functions as a planarization layer. Note that the number of insulating layers covering the transistor is not limited and may be one or two or more.

A material through which impurities such as water or hydrogen do not easily diffuse is preferably used for at least one of the insulating layers that cover the transistors. This is because such an insulating layer can serve as a barrier film. Such a structure can effectively suppress diffusion of the impurities into the transistors from the outside, and a highly reliable display device can be provided.

Each of the transistors 201, 203, 205, and 206 includes a conductive layer 221 a functioning as a gate, the insulating layer 211 functioning as the gate insulating layer, the conductive layer 222 a and a conductive layer 222 b functioning as a source and a drain, and a semiconductor layer 231. Here, a plurality of layers obtained by processing the same conductive film are shown with the same hatching pattern.

The transistor 201 and the transistor 205 each include a conductive layer 223 functioning as a gate, in addition to the components of the transistor 203 or the transistor 206.

The structure in which the semiconductor layer where a channel is formed is provided between two gates is used as an example of the transistors 201 and 205. Such a structure enables the control of the threshold voltages of transistors. The two gates may be connected to each other and supplied with the same signal to operate the transistors. Such transistors can have higher field-effect mobility and thus have higher on-state current than other transistors. Consequently, a circuit capable of high-speed operation can be obtained. Furthermore, the area occupied by a circuit portion can be reduced. The use of the transistor having high on-state current can reduce signal delay in wirings and can reduce display unevenness even in a display device in which the number of wirings is increased because of increase in size or definition.

Alternatively, by supplying a potential for controlling the threshold voltage to one of the two gates and a potential for driving to the other, the threshold voltage of the transistors can be controlled.

There is no limitation of the structure of the transistors included in the display device. The transistor included in the circuit 364 and the transistor included in the display portion 362 may have the same structure or different structures. A plurality of transistors included in the circuit 364 may have the same structure or a combination of two or more kinds of structures. Similarly, a plurality of transistors included in the display portion 362 may have the same structure or a combination of two or more kinds of structures.

It is preferable to use a conductive material containing an oxide for the conductive layer 223. A conductive film used for the conductive layer 223 is formed under an atmosphere containing oxygen, whereby oxygen can be supplied to the insulating layer 212. The proportion of an oxygen gas in a deposition gas is preferably higher than or equal to 90% and lower than or equal to 100%. Oxygen supplied to the insulating layer 212 is then supplied to the semiconductor layer 231 by later heat treatment; as a result, oxygen vacancies in the semiconductor layer 231 can be reduced.

It is particularly preferable to use a low-resistance oxide semiconductor for the conductive layer 223. In that case, an insulating film that releases hydrogen, such as a silicon nitride film, is preferably used for the insulating layer 213, for example, because hydrogen can be supplied to the conductive layer 223 during the formation of the insulating layer 213 or by heat treatment performed after the formation of the insulating layer 213, which leads to an effective reduction in the electric resistance of the conductive layer 223.

The coloring layer 134 is provided in contact with the insulating layer 213. The coloring layer 134 is covered with the insulating layer 214.

A connection portion 204 is provided in a region where the substrate 351 and the substrate 361 do not overlap with each other. In the connection portion 204, the wiring 365 is electrically connected to the FPC 372 via a connection layer 242. The connection portion 204 has a similar structure to the connection portion 207. On the top surface of the connection portion 204, a conductive layer 311 b is exposed. The electrode 311 a and the conductive layer 311 b are formed by processing the same conductive film. The connection layer 242 is preferably provided to cover an end portion of the conductive layer 311 b. Accordingly, the connection portion 204 and the FPC 372 can be electrically connected to each other via the connection layer 242.

As the polarizing plate 135 provided on the outer surface of the substrate 361, a linear polarizing plate or a circularly polarizing plate can be used. An example of a circularly polarizing plate is a stack including a linear polarizing plate and a quarter-wave retardation plate. Such a structure can reduce reflection of external light. The cell gap, alignment, drive voltage, and the like of the liquid crystal element used as the liquid crystal element 180 are controlled depending on the kind of the polarizing plate so that desirable contrast is obtained.

Note that a variety of optical members can be arranged on the outer surface of the substrate 361. Examples of the optical members include a polarizing plate, a retardation plate, a light diffusion layer (e.g., a diffusion film), an anti-reflective layer, and a light-condensing film. Furthermore, an antistatic film preventing the attachment of dust, a water repellent film suppressing the attachment of stain, a hard coat film suppressing generation of a scratch caused by the use, or the like may be arranged on the outer surface of the substrate 361.

For each of the substrates 351 and 361, glass, quartz, ceramic, sapphire, an organic resin, or the like can be used. When the substrates 351 and 361 are formed using a flexible material, the flexibility of the display device can be increased. In particular, when the substrates 351 and 361 are formed using an organic resin, the thickness and weight of the display device can be reduced.

A liquid crystal element having, for example, a vertical alignment (VA) mode can be used as the liquid crystal element 180. Examples of the vertical alignment mode include a multi-domain vertical alignment (MVA) mode, a patterned vertical alignment (PVA) mode, and an advanced super view (ASV) mode.

A liquid crystal element having a variety of modes can be used as the liquid crystal element 180. For example, a liquid crystal element using, instead of a VA mode, a twisted nematic (TN) mode, an in-plane switching (IPS) mode, a fringe field switching (FFS) mode, an axially symmetric aligned micro-cell (ASM) mode, an optically compensated birefringence (OCB) mode, a ferroelectric liquid crystal (FLC) mode, an antiferroelectric liquid crystal (AFLC) mode, or the like can be used.

The liquid crystal element is an element that controls transmission or non-transmission of light utilizing an optical modulation action of the liquid crystal. The optical modulation action of the liquid crystal is controlled by an electric field applied to the liquid crystal (including a horizontal electric field, a vertical electric field, and an oblique electric field). As the liquid crystal used for the liquid crystal element, a thermotropic liquid crystal, a low-molecular liquid crystal, a high-molecular liquid crystal, a polymer dispersed liquid crystal (PDLC), a ferroelectric liquid crystal, an anti-ferroelectric liquid crystal, or the like can be used. Such a liquid crystal material exhibits a cholesteric phase, a smectic phase, a cubic phase, a chiral nematic phase, an isotropic phase, or the like depending on conditions.

As the liquid crystal material, a positive liquid crystal or a negative liquid crystal may be used, and an appropriate liquid crystal material can be used depending on the mode or design to be used.

To control the alignment of the liquid crystal, the alignment films can be provided. In the case where a horizontal electric field mode is employed, a liquid crystal exhibiting a blue phase for which an alignment film is unnecessary may be used. The blue phase is one of liquid crystal phases, which is generated just before a cholesteric phase changes into an isotropic phase while the temperature of a cholesteric liquid crystal is increased. Since the blue phase appears only in a narrow temperature range, a liquid crystal composition in which several weight percent or more of a chiral material is mixed is used for the liquid crystal in order to improve the temperature range. The liquid crystal composition that includes a liquid crystal exhibiting a blue phase and a chiral material has a short response time and has optical isotropy. In addition, the liquid crystal composition that includes a liquid crystal exhibiting a blue phase and a chiral material does not need alignment treatment and has small viewing angle dependence. An alignment film does not need to be provided and rubbing treatment is thus not necessary; accordingly, electrostatic discharge damage caused by the rubbing treatment can be prevented and defects and damage of the liquid crystal display device in the manufacturing process can be reduced.

In the case where the reflective liquid crystal element is used, the polarizing plate 135 is provided on the display surface side. In addition, a light diffusion plate is preferably provided on the display surface side to improve visibility.

A front light may be provided on the outer side of the polarizing plate 135. As the front light, an edge-light front light is preferably used. A front light including an LED is preferably used to reduce power consumption.

As the adhesive layer, any of a variety of curable adhesives such as a reactive curable adhesive, a thermosetting adhesive, an anaerobic adhesive, and a photocurable adhesive such as an ultraviolet curable adhesive can be used. Examples of these adhesives include an epoxy resin, an acrylic resin, a silicone resin, a phenol resin, a polyimide resin, an imide resin, a polyvinyl chloride (PVC) resin, a polyvinyl butyral (PVB) resin, and an ethylene vinyl acetate (EVA) resin. In particular, a material with low moisture permeability, such as an epoxy resin, is preferred. Alternatively, a two-component-mixture-type resin may be used. Further alternatively, an adhesive sheet or the like may be used.

As the connection layer 242, an anisotropic conductive film (ACF), an anisotropic conductive paste (ACP), or the like can be used.

The light-emitting element 170 may be a top emission, bottom emission, or dual emission light-emitting element, or the like. A conductive film that transmits visible light is used as the electrode through which light is extracted. A conductive film that reflects visible light is preferably used as the electrode through which light is not extracted.

The EL layer 192 includes at least a light-emitting layer. In addition to the light-emitting layer, the EL layer 192 may further include one or more layers containing any of a substance with a high hole-injection property, a substance with a high hole-transport property, a hole-blocking material, a substance with a high electron-transport property, a substance with a high electron-injection property, a substance with a bipolar property (a substance with a high electron- and hole-transport property), and the like.

Either a low molecular compound or a high molecular compound can be used for the EL layer 192, and an inorganic compound may also be included. The layers included in the EL layer 192 can be formed by any of the following methods: an evaporation method (including a vacuum evaporation method), a transfer method, a printing method, an inkjet method, a coating method, and the like.

The EL layer 192 may contain an inorganic compound such as quantum dots. When quantum dots are used for the light-emitting layer, quantum dots can function as light-emitting materials, for example.

With the use of the combination of a color filter (coloring layer) and a microcavity structure (optical adjustment layer), light with high color purity can be extracted from the display device. The thickness of the optical adjustment layer varies depending on the color of the pixel.

As materials for a gate, a source, and a drain of a transistor, and a conductive layer such as a wiring or an electrode included in a display device, any of metals such as aluminum, titanium, chromium, nickel, copper, yttrium, zirconium, molybdenum, silver, tantalum, and tungsten, or an alloy containing any of these metals as its main component can be used. A single-layer structure or multi-layer structure including a film containing any of these materials can be used.

As a light-transmitting conductive material, a conductive oxide such as indium oxide, indium tin oxide (ITO), indium zinc oxide, zinc oxide, or zinc oxide containing gallium, or graphene can be used. Alternatively, a metal material such as gold, silver, platinum, magnesium, nickel, tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, or titanium, or an alloy material containing any of these metal materials can be used. Alternatively, a nitride of the metal material (e.g., titanium nitride) or the like may be used. In the case of using the metal material or the alloy material (or the nitride thereof), the thickness is set small enough to be able to transmit light. Alternatively, a stacked film of any of the above materials can be used for the conductive layers. For example, a stacked film of indium tin oxide and an alloy of silver and magnesium is preferably used because the conductivity can be increased. They can also be used for conductive layers such as a variety of wirings and electrodes included in a display device, and conductive layers (e.g., conductive layers serving as a pixel electrode or a common electrode) included in a display element.

Examples of an insulating material that can be used for the insulating layers include a resin such as acrylic or epoxy resin, and an inorganic insulating material such as silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, or aluminum oxide.

Examples of a material that can be used for the coloring layers include a metal material, a resin material, and a resin material containing a pigment or dye.

Structure Example 2

A display device 300A illustrated in FIG. 3 is different from the display device 300 mainly in that a transistor 281, a transistor 284, a transistor 285, and a transistor 286 are included instead of the transistor 201, the transistor 203, the transistor 205, and the transistor 206.

Note that the positions of the insulating layer 117, the connection portion 207, and the like in FIG. 3 are different from those in FIG. 2. FIG. 3 illustrates an end portion of a pixel. The insulating layer 117 is provided so as to overlap with an end portion of the coloring layer 131 and an end portion of the light-blocking layer 132. As in this structure, at least part of the insulating layer 117 may be provided in a region not overlapping with a display region (or in a region overlapping with the light-blocking layer 132).

Two transistors included in the display device may partly overlap with each other like the transistor 284 and the transistor 285. In that case, the area occupied by a pixel circuit can be reduced, leading to an increase in resolution. Furthermore, the light-emitting area of the light-emitting element 170 can be increased, leading to an improvement in aperture ratio. The light-emitting element 170 with a high aperture ratio requires low current density to obtain necessary luminance; thus, the reliability is improved.

Each of the transistors 281, 284, and 286 includes the conductive layer 221 a, the insulating layer 211, the semiconductor layer 231, the conductive layer 222 a, and the conductive layer 222 b. The conductive layer 221 a overlaps with the semiconductor layer 231 with the insulating layer 211 positioned therebetween. The conductive layer 222 a and the conductive layer 222 b are electrically connected to the semiconductor layer 231. The transistor 281 includes the conductive layer 223.

The transistor 285 includes the conductive layer 222 a, an insulating layer 217, a semiconductor layer 261, the conductive layer 223, the insulating layer 212, the insulating layer 213, a conductive layer 263 a, and a conductive layer 263 b. The conductive layer 222 a overlaps with the semiconductor layer 261 with the insulating layer 217 positioned therebetween. The conductive layer 223 overlaps with the semiconductor layer 261 with the insulating layers 212 and 213 positioned therebetween. The conductive layer 263 a and the conductive layer 263 b are electrically connected to the semiconductor layer 261.

The conductive layer 221 a functions as a gate. The insulating layer 211 functions as a gate insulating layer. The conductive layer 222 a functions as one of a source and a drain. The conductive layer 222 b included in the transistor 286 functions as the other of the source and the drain.

The conductive layer 222 a shared by the transistor 284 and the transistor 285 has a portion functioning as one of a source and a drain of the transistor 284 and a portion functioning as a gate of the transistor 285. The insulating layer 217, the insulating layer 212, and the insulating layer 213 function as gate insulating layers. One of the conductive layer 263 a and the conductive layer 263 b functions as a source and the other functions as a drain. The conductive layer 223 functions as a gate.

Structure Example 3

FIG. 4A is a cross-sectional view illustrating a display portion of a display device 300B.

The display device 300B is different from the display device 300 in that the coloring layer 131 is not provided. The transistor 203 is not illustrated in FIG. 4A. Other components are similar to those of the display device 300 and thus are not described in detail.

The liquid crystal element 180 emits white light. Since the coloring layer 131 is not provided, the display device 300B can display a black-and-white image or a grayscale image using the liquid crystal element 180.

The display device 300B is an example in which the substrate 361 is provided with the electrode 113 with the insulating layer 121 positioned therebetween. The insulating layer 121 is not necessarily provided, and the electrode 113 may be provided in contact with the substrate 361 as in a display device 300C illustrated in FIG. 4B.

Structure Example 4

The display device 300C illustrated in FIG. 4B is different from the display device 300B in that the EL layer 192 is separately provided for each color and in that the coloring layer 134 and the insulating layer 121 are not provided. Other components are similar to those of the display device 300B and thus are not described in detail.

In the light-emitting element 170 employing a separate coloring method, at least one layer (typified by the light-emitting layer) included in the EL layer 192 is separately provided for each color. All layers included in the EL layer may be separately provided for each color.

Example 1 of Manufacturing Method of Display Device

Next, the method for manufacturing the display device of this embodiment will be specifically described with reference to FIGS. 5A, 5B1, 5B2, and 5C, FIGS. 6A to 6C, FIGS. 7A to 7C, and FIGS. 8A and 8B. An example of a manufacturing method of the display device 300 illustrated in FIG. 2 will be described below. The manufacturing method will be described with reference to FIGS. 5A, 5B1, 5B2, and 5C, FIGS. 6A to 6C, FIGS. 7A to 7C, and FIGS. 8A and 8B, focusing on the display portion 362 and the connection portion 204 of the display device 300. Note that the transistor 203 is not illustrated in FIGS. 5A, 5B1, 5B2, and 5C, FIGS. 6A to 6C, FIGS. 7A to 7C, and FIGS. 8A and 8B.

Thin films included in the display device (e.g., insulating films, semiconductor films, or conductive films) can be formed by any of a sputtering method, a chemical vapor deposition (CVD) method, a vacuum evaporation method, a pulsed laser deposition (PLD) method, an atomic layer deposition (ALD) method, and the like. As the CVD method, a plasma-enhanced chemical vapor deposition (PECVD) method or a thermal CVD method may be used. As the thermal CVD method, for example, a metal organic chemical vapor deposition (MOCVD) method may be used.

Alternatively, thin films included in the display device (e.g., insulating films, semiconductor films, or conductive films) can be formed by a method such as spin coating, dipping, spray coating, ink-jetting, dispensing, screen printing, or offset printing, or with a doctor knife, a slit coater, a roll coater, a curtain coater, or a knife coater.

When thin films included in the display device are processed, a lithography method or the like can be used for the processing. Alternatively, island-shaped thin films may be formed by a film formation method using a blocking mask. A nanoimprinting method, a sandblasting method, a lift-off method, or the like may be used for the processing of thin films. Examples of a photolithography method include a method in which a resist mask is formed over a thin film to be processed, the thin film is processed by etching or the like, and the resist mask is removed, and a method in which a photosensitive thin film is formed and exposed to light and developed to be processed into a desired shape.

In the case of using light in the lithography method, any of an i-line (light with a wavelength of 365 nm), a g-line (light with a wavelength of 436 nm), and an h-line (light with a wavelength of 405 nm), or combined light of any of them can be used for exposure. Alternatively, ultraviolet light, KrF laser light, ArF laser light, or the like can be used. Exposure may be performed by liquid immersion exposure technique. As the light for the exposure, extreme ultra-violet (EUV) light or X-rays may be used. Instead of the light for the exposure, an electron beam can be used. It is preferable to use EUV, X-rays, or an electron beam because extremely minute processing can be performed. Note that in the case of performing exposure by scanning of a beam such as an electron beam, a photomask is not needed.

For etching of thin films, a dry etching method, a wet etching method, a sandblast method, or the like can be used.

First, the coloring layer 131 is formed over the substrate 361 (FIG. 5A). The coloring layer 131 is formed using a photosensitive material, in which case the processing into an island shape can be performed by a photolithography method or the like. Note that in the circuit 364 and the like illustrated in FIG. 2, the light-blocking layer 132 is provided over the substrate 361.

Then, the insulating layer 121 is formed over the coloring layer 131 and the light-blocking layer 132.

The insulating layer 121 preferably functions as a planarization layer. An organic insulating film is preferably used for the insulating layer 121. A resin such as acrylic or epoxy is suitably used for the insulating layer 121.

An inorganic insulating film may be used for the insulating layer 121. For example, an inorganic insulating film such as a silicon nitride film, a silicon oxynitride film, a silicon oxide film, a silicon nitride oxide film, an aluminum oxide film, or an aluminum nitride film can be used for the insulating layer 121. Alternatively, a hafnium oxide film, an yttrium oxide film, a zirconium oxide film, a gallium oxide film, a tantalum oxide film, a magnesium oxide film, a lanthanum oxide film, a cerium oxide film, a neodymium oxide film, or the like may be used. Further alternatively, a stack including two or more of the above insulating films may be used.

Next, the electrode 113 is formed. The electrode 113 can be formed in the following manner: a conductive film is formed, a resist mask is formed, the conductive film is etched, and the resist mask is removed. The electrode 113 is formed using a conductive material that transmits visible light.

After that, the insulating layer 117 is formed over the electrode 113. An organic insulating film is preferably used for the insulating layer 117. A resin such as acrylic or epoxy is suitably used for the insulating layer 117.

Subsequently, the alignment film 133 b is formed over the electrode 113 and the insulating layer 117 (FIG. 5A). The alignment film 133 b can be formed in the following manner: a thin film is formed using a resin or the like, and then, rubbing treatment is performed.

Note that steps illustrated in FIGS. 5B1, 5B2, and 5C, FIGS. 6A to 6C, FIGS. 7A to 7C, and FIG. 8A are performed independently of the steps described with reference to FIG. 5A.

First, a separation layer 311 is formed over a formation substrate 350 (FIG. 5B1). In the step illustrated in FIG. 5B1, a material is selected that would cause separation at the interface between the formation substrate 350 and the separation layer 311 when the formation substrate 350 is peeled.

Alternatively, an insulating layer 355 is formed over the formation substrate 350 and the separation layer 311 is formed over the insulating layer 355 (FIG. 5B2). In the step illustrated in FIG. 5B2, a material is selected that would cause separation at the interface between the insulating layer 355 and the separation layer 311 when the formation substrate 350 is peeled.

The formation substrate 350 has stiffness high enough for easy transfer and has resistance to heat applied in the manufacturing process. Examples of a material that can be used for the formation substrate 350 include glass, quartz, ceramic, sapphire, a resin, a semiconductor, a metal, and an alloy. Examples of the glass include alkali-free glass, barium borosilicate glass, and aluminoborosilicate glass.

The separation layer 311 can be formed using, for example, nickel (Ni), titanium (Ti), silver (Ag), or an alloy containing any of these elements.

The position of an interface where peeling is performed in the separation step depends on the material of the separation layer 311. Thus, the selection of the material of the separation layer 311 is important. For example, when tungsten (W) or molybdenum (Mo) is used for the separation layer, the separation layer remains on the formation substrate side in many cases. In this embodiment, the separation layer 311 is formed using nickel (Ni), titanium (Ti), silver (Ag), or an alloy containing any of these elements. The use of such a material allows separation between the formation substrate 350 and the separation layer 311 at the time of peeling (the separation layer 311 hardly remains on the formation substrate 350 side).

In Example 1 of manufacturing method of display device, the electrode 311 a is formed using the separation layer 311 in a later step; thus, it is preferable to use a material with high visible light reflexibility for the separation layer 311.

The thickness of the separation layer 311 is preferably greater than or equal to 10 nm and less than or equal to 1000 nm, and further preferably greater than or equal to 10 nm and less than or equal to 500 nm.

When a glass substrate is used for the formation substrate 350 and a nickel film is used for the separation layer 311 in FIG. 5B1, for example, separation can occur in the separation step at the interface between the formation substrate 350 and the separation layer 311. The peelability can be increased particularly when the maximum temperature applied to the separation layer 311 is higher than 150° C. and lower than 450° C., preferably higher than or equal to 200° C. and lower than or equal to 400° C., and further preferably higher than or equal to 250° C. and lower than or equal to 350° C. For this reason, the maximum temperature applied to the separation layer 311 in steps of forming a transistor and a display element over the separation layer 311 is preferably within the above range.

When the insulating layer 355 has a three-layer structure described below and a titanium film is used for the separation layer 311 in FIG. 5B2, for example, separation can be caused in the separation step at the interface between the insulating layer 355 and the separation layer 311.

In the case where a titanium film is used for the separation layer 311 and an oxide film (an oxide insulating film or an oxide conductive film such as an ITO film or the like) is formed on the titanium film, the quality of the separation layer 311 is changed (e.g., titanium is oxidized) and the peelability is decreased when the temperature of a later heating step is too high, in some cases. The quality change in titanium can be inhibited and the peelability can be increased when the maximum temperature applied to the separation layer 311 is lower than 450° C., preferably lower than or equal to 400° C., and further preferably lower than or equal to 350° C. For this reason, the maximum temperature applied to the separation layer 311 in the steps of forming the transistor and the display element over the separation layer 311 is preferably within the above range.

The insulating layer 355 preferably includes a first insulating layer over the formation substrate 350, a second insulating layer over the first insulating layer, and a third insulating layer over the second insulating layer, for example.

The first insulating layer has a function of blocking hydrogen and fluorine (and nitrogen) released from the second insulating layer and the third insulating layer in the later heating step.

The first insulating layer preferably contains nitrogen and silicon. For the first insulating layer, for example, a silicon nitride film, a silicon oxynitride film, or a silicon nitride oxide film can be used. It is particularly preferable to use a silicon nitride film or a silicon nitride oxide film.

The first insulating layer can be formed by a sputtering method, a plasma CVD method, or the like. For the first insulating layer, for example, a silicon nitride film is formed by a plasma CVD method using a deposition gas containing a silane (SiH₄) gas, a hydrogen gas, and an ammonia (NH₃) gas.

There is no particular limitation on the thickness of the first insulating layer. The thickness can be greater than or equal to 50 nm and less than or equal to 600 nm, and preferably greater than or equal to 100 nm and less than or equal to 300 nm, for example.

Note that in the case where the formation substrate has a sufficiently high blocking property against hydrogen and fluorine (and nitrogen), the first insulating layer does not always need to be provided. In that case, the second insulating layer may be provided on the formation substrate.

The second insulating layer has a function of releasing hydrogen in the later heating step. The second insulating layer may also have a function of releasing hydrogen and nitrogen in the later heating step.

The second insulating layer preferably contains oxygen and silicon. It is preferable that the second insulating layer further contain hydrogen. It is preferable that the second insulating layer further contain nitrogen. For the second insulating layer, for example, a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or a silicon nitride oxide film can be used.

The second insulating layer can be formed by a sputtering method, a plasma CVD method, or the like. It is particularly preferable to form the silicon oxynitride film by a plasma CVD method using a deposition gas containing a silane gas and a nitrous oxide (N₂O) gas because a large amount of hydrogen and nitrogen can be contained in the film. In addition, the proportion of the silane gas in the deposition gas is preferably higher, in which case the amount of released hydrogen in the later heating step is increased.

The thickness of the second insulating layer is preferably larger for an increase in the amount of released hydrogen and nitrogen; however, the thickness is preferably determined in consideration of productivity. The thickness of the second insulating layer is preferably greater than or equal to 1 nm and less than or equal to 1 μm, further preferably greater than or equal to 50 nm and less than or equal to 800 nm, still further preferably greater than or equal to 100 nm and less than or equal to 600 nm, and particularly preferably greater than or equal to 200 nm and less than or equal to 400 nm.

At least one of the first insulating layer and the second insulating layer can serve as a base film. In the case where a glass substrate is used as the formation substrate 350, for example, a base film is preferably provided between the formation substrate 350 and the separation layer 311 because contamination from the glass substrate can be prevented.

The third insulating layer has a function of releasing fluorine in the later heating step. The third insulating layer also has a function of allowing hydrogen (and nitrogen) released from the second insulating layer to pass through.

The third insulating layer preferably contains oxygen, fluorine, and silicon. For the third insulating layer, for example, a silicon oxide film containing fluorine (SiOF) can be used.

The third insulating layer can be formed by a sputtering method, a plasma CVD method, or the like. For the third insulating layer, for example, a silicon oxide film containing fluorine is formed by a plasma CVD method using a deposition gas containing a silane gas, a nitrous oxide gas, and a silicon tetrafluoride (SiF₄) gas.

The third insulating layer preferably has a thickness greater than or equal to 1 nm and less than or equal to 500 nm, further preferably greater than or equal to 10 nm and less than or equal to 300 nm, and still further preferably greater than or equal to 10 nm and less than or equal to 200 nm. The third insulating layer can have a smaller thickness than the second insulating layer.

After the insulating layer 355 and the separation layer 311 are formed over the formation substrate 350, heat treatment is performed. The heat treatment is preferably performed after the insulating layer 220 is formed over the separation layer 311. For example, the heat treatment is preferably performed after the insulating layer 220 is formed before the transistor is formed. Heat treatment performed in the step of forming the transistor may serve as this heat treatment.

Owing to the heat treatment, hydrogen (and nitrogen) is released from the second insulating layer and supplied to the separation layer 311 (or the interface between the third insulating layer and the separation layer 311) through the third insulating layer. In addition, fluorine is released from the third insulating layer and supplied to the separation layer 311 (or the interface between the third insulating layer and the separation layer 311). At this time, the first insulating layer and the insulating layer 220 block the released hydrogen and fluorine (and nitrogen), leading to efficient supply of hydrogen and fluorine (and nitrogen) to the separation layer 311 (or the interface between the third insulating layer and the separation layer 311).

The atmosphere in which the heat treatment is performed is not particularly limited and may be an air atmosphere. It is preferable to perform the heat treatment in an inert gas atmosphere such as a nitrogen atmosphere or a rare gas atmosphere.

The following description is for the case of employing the step illustrated in FIG. 5B1. Note that the following description can also be applied to the case of employing the step illustrated in FIG. 5B2.

The insulating layer 220 is formed (FIG. 5C). Then, openings that reach the separation layer 311 are provided in the insulating layer 220. To prevent the separation layer 311 from being removed, it is preferable that the etching selectivity ratio of the insulating layer 220 to the separation layer 311 be sufficiently large.

The insulating layer 220 can be used as a barrier layer that prevents diffusion of impurities into the transistor and the display element formed later.

The insulating layer 220 can be formed using the inorganic insulating film, the resin, or the like that can be used for the insulating layer 121. It is particularly preferable to use a silicon nitride film.

Next, the connection portion 204, the connection portion 207, the transistor 205, and the transistor 206 are formed over the insulating layer 220.

There is no particular limitation on a semiconductor material used for a semiconductor layer of the transistor, and for example, a Group 14 element, a compound semiconductor, or an oxide semiconductor can be used. Typically, a semiconductor containing silicon, a semiconductor containing gallium arsenide, an oxide semiconductor containing indium, or the like can be used.

It is preferable to use an oxide semiconductor for a channel formation region of the transistor. With the use of an oxide semiconductor, the maximum process temperature can be lower than that in the case of using low-temperature polysilicon (LTPS). Specifically, the transistor formed using an oxide semiconductor does not require heat treatment at high temperatures unlike a transistor formed using LTPS, and can be formed at a temperature lower than or equal to 350° C., or even lower than or equal to 300° C. Even without heat treatment at high temperatures, a highly reliable transistor can be formed and the peelability between the formation substrate 350 (typified by a glass substrate) and the separation layer 311 (typified by nickel) can be increased. Furthermore, even without heat treatment at high temperatures, a highly reliable transistor can be formed, the quality change in the separation layer 311 (typified by titanium) can be inhibited, and the peelability can be increased.

Here, the case where a bottom-gate transistor including an oxide semiconductor layer as the semiconductor layer 231 is fabricated as the transistor 206 is described. The transistor 205 includes the conductive layer 223 and the insulating layer 212 in addition to the components of the transistor 206, and has two gates.

An oxide semiconductor is preferably used for the semiconductor layer of the transistor. The use of a semiconductor material having a wider band gap and a lower carrier density than silicon can reduce off-state current of the transistor.

Specifically, first, the conductive layer 221 a, the conductive layer 221 b, and a conductive layer 221 c are formed over the insulating layer 220. The conductive layer 221 a, the conductive layer 221 b, and the conductive layer 221 c can be formed in the following manner: a conductive film is formed, a resist mask is formed, the conductive film is etched, and the resist mask is removed. At this time, the conductive layer 221 b and the separation layer 311 are connected to each other through an opening in the insulating layer 220 at the connection portion 207, and the conductive layer 221 c and the separation layer 311 are connected to each other through an opening in the insulating layer 220 at the connection portion 204.

When the conductive layer 221 b and the conductive layer 221 c are connected to the separation layer 311, an adverse effect of electrostatic charge due to peeling can be inhibited.

Next, the insulating layer 211 is formed.

For the insulating layer 211, an inorganic insulating film such as a silicon nitride film, a silicon oxynitride film, a silicon oxide film, a silicon nitride oxide film, an aluminum oxide film, or an aluminum nitride film can be used, for example. Alternatively, a hafnium oxide film, an yttrium oxide film, a zirconium oxide film, a gallium oxide film, a tantalum oxide film, a magnesium oxide film, a lanthanum oxide film, a cerium oxide film, a neodymium oxide film, or the like may be used. Further alternatively, a stack including two or more of the above insulating films may be used.

An inorganic insulating film is preferably formed at high temperatures because the film can have higher density and a higher barrier property as the deposition temperature becomes higher. The substrate temperature during the deposition of the inorganic insulating film is preferably higher than or equal to room temperature (25° C.) and lower than or equal to 350° C., and further preferably higher than or equal to 100° C. and lower than or equal to 300° C.

Then, the semiconductor layer 231 is formed. In this embodiment, an oxide semiconductor layer is formed as the semiconductor layer 231. The oxide semiconductor layer can be formed in the following manner: an oxide semiconductor film is formed, a resist mask is formed, the oxide semiconductor film is etched, and the resist mask is removed.

The substrate temperature during the deposition of the oxide semiconductor film is preferably lower than or equal to 350° C., further preferably higher than or equal to room temperature and lower than or equal to 200° C., and still further preferably higher than or equal to room temperature and lower than or equal to 130° C.

The oxide semiconductor film can be formed using one or both of an inert gas and an oxygen gas. Note that there is no particular limitation on the percentage of oxygen flow rate (partial pressure of oxygen) at the time of forming the oxide semiconductor film. To fabricate a transistor having high field-effect mobility, however, the percentage of oxygen flow rate (partial pressure of oxygen) at the time of forming the oxide semiconductor film is preferably higher than or equal to 0% and lower than or equal to 30%, further preferably higher than or equal to 5% and lower than or equal to 30%, and still further preferably higher than or equal to 7% and lower than or equal to 15%.

The oxide semiconductor film preferably contains at least indium or zinc. It is particularly preferable to contain indium and zinc.

The energy gap of the oxide semiconductor is preferably 2 eV or more, further preferably 2.5 eV or more, and still further preferably 3 eV or more. The use of such an oxide semiconductor having a wide energy gap leads to a reduction in off-state current of a transistor.

The oxide semiconductor film can be formed by a sputtering method. Alternatively, a PLD method, a PECVD method, a thermal CVD method, an ALD method, a vacuum evaporation method, or the like may be used.

Note that an example of an oxide semiconductor will be described in Embodiment 3.

Next, the conductive layers 222 a and 222 b and the wiring 365 are formed. The conductive layers 222 a and 222 b and the wiring 365 can be formed in the following manner: a conductive film is formed, a resist mask is formed, the conductive film is etched, and the resist mask is removed. Each of the conductive layers 222 a and 222 b is connected to the semiconductor layer 231. Here, the conductive layer 222 a included in the transistor 206 is electrically connected to the conductive layer 221 b. As a result, the separation layer 311 and the conductive layer 222 a can be electrically connected to each other at the connection portion 207. At the connection portion 204, the wiring 365 and the separation layer 311 are electrically connected to each other with the conductive layer 221 c provided therebetween.

Note that during the processing of the conductive layer 222 a and the conductive layer 222 b, the semiconductor layer 231 might be partly etched to be thin in a region not covered by the resist mask.

In the above manner, the transistor 206 can be fabricated (FIG. 5C). In the transistor 206, part of the conductive layer 221 a functions as a gate, part of the insulating layer 211 functions as a gate insulating layer, and the conductive layer 222 a and the conductive layer 222 b each function as one of a source and a drain.

Next, the insulating layer 212 that covers the transistor 206 is formed, and the conductive layer 223 is formed over the insulating layer 212.

The insulating layer 212 can be formed in a manner similar to that of the insulating layer 211.

The conductive layer 223 included in the transistor 205 can be formed in the following manner: a conductive film is formed, a resist mask is formed, the conductive film is etched, and the resist mask is removed.

In the above manner, the transistor 205 can be fabricated (FIG. 5C). In the transistor 205, part of the conductive layer 221 a and part of the conductive layer 223 function as gates, part of the insulating layer 211 and part of the insulating layer 212 function as gate insulating layers, and the conductive layer 222 a and the conductive layer 222 b each function as a source or a drain.

Next, the insulating layer 213 is formed (FIG. 5C). The insulating layer 213 can be formed in a manner similar to that of the insulating layer 211.

It is preferable to use an oxide insulating film formed in an atmosphere containing oxygen, such as a silicon oxide film or a silicon oxynitride film, for the insulating layer 212. An insulating film with low oxygen diffusibility and oxygen permeability, such as a silicon nitride film, is preferably stacked as the insulating layer 213 over the silicon oxide film or the silicon oxynitride film. The oxide insulating film formed in an atmosphere containing oxygen can easily release a large amount of oxygen by heating. When a stack including such an oxide insulating film that releases oxygen and an insulating film with low oxygen diffusibility and oxygen permeability is heated, oxygen can be supplied to the oxide semiconductor layer. As a result, oxygen vacancies in the oxide semiconductor layer can be filled and defects at the interface between the oxide semiconductor layer and the insulating layer 212 can be repaired, leading to a reduction in defect levels. Accordingly, an extremely highly reliable display device can be fabricated.

Next, the coloring layer 134 is formed over the insulating layer 213 (FIG. 5C), and then, the insulating layer 214 is formed (FIG. 6A).

The coloring layer 134 can be formed in a manner similar to that of the coloring layer 131. The display element is formed on the insulating layer 214 in a later step; thus, the insulating layer 214 preferably functions as a planarization layer. For the insulating layer 214, the description of the resin or the inorganic insulating film that can be used for the insulating layer 121 can be referred to.

After that, an opening that reaches the conductive layer 222 a included in the transistor 205 is formed in the insulating layer 212, the insulating layer 213, and the insulating layer 214.

Subsequently, the electrode 191 is formed (FIG. 6A). The electrode 191 can be formed in the following manner: a conductive film is formed, a resist mask is formed, the conductive film is etched, and the resist mask is removed. Here, the conductive layer 222 a included in the transistor 205 and the electrode 191 are connected to each other. The electrode 191 is formed using a conductive material that transmits visible light.

Then, the insulating layer 216 that covers the end portion of the electrode 191 is formed (FIG. 6A). For the insulating layer 216, the description of the resin or the inorganic insulating film that can be used for the insulating layer 121 can be referred to. The insulating layer 216 includes an opening in a region overlapping with the electrode 191.

Next, the EL layer 192 and the electrode 193 are formed (FIG. 6B). Part of the electrode 193 functions as the common electrode of the light-emitting element 170. The electrode 193 is formed using a conductive material that reflects visible light.

The EL layer 192 can be formed by an evaporation method, a coating method, a printing method, a discharge method, or the like. In the case where the EL layer 192 is formed for each individual pixel, an evaporation method using a blocking mask such as a metal mask, an ink-jet method, or the like can be used. In the case of sharing the EL layer 192 by some pixels, an evaporation method not using a metal mask can be used.

Either a low molecular compound or a high molecular compound can be used for the EL layer 192, and an inorganic compound may also be included.

Steps after the formation of the EL layer 192 are performed such that temperatures higher than the heat resistant temperature of the EL layer 192 are not applied to the EL layer 192. The electrode 193 can be formed by an evaporation method, a sputtering method, or the like.

In the above manner, the light-emitting element 170 can be formed (FIG. 6B). In the light-emitting element 170, the electrode 191 part of which functions as the pixel electrode, the EL layer 192, and the electrode 193 part of which functions as the common electrode are stacked. The light-emitting element 170 is formed such that the light-emitting region overlaps with the coloring layer 134.

Although an example where a bottom-emission light-emitting element is formed as the light-emitting element 170 is described here, one embodiment of the present invention is not limited thereto.

The light-emitting element may be a top emission, bottom emission, or dual emission light-emitting element. A conductive film that transmits visible light is used as the electrode through which light is extracted. A conductive film that reflects visible light is preferably used as the electrode through which light is not extracted.

Next, the insulating layer 194 is formed so as to cover the electrode 193 (FIG. 6B). The insulating layer 194 functions as a protective layer that prevents diffusion of impurities such as water into the light-emitting element 170. The light-emitting element 170 is sealed with the insulating layer 194. After the electrode 193 is formed, the insulating layer 194 is preferably formed without exposure to the air.

The inorganic insulating film that can be used for the insulating layer 121 can be used for the insulating layer 194, for example. It is particularly preferable that an inorganic insulating film with a high barrier property be included. A stack including an inorganic insulating film and an organic insulating film can also be used.

The insulating layer 194 is preferably formed at substrate temperature lower than or equal to the heat resistant temperature of the EL layer 192. The insulating layer 194 can be formed by an ALD method, a sputtering method, or the like. An ALD method and a sputtering method are preferable because a film can be formed at low temperatures. An ALD method is preferable because the coverage of the insulating layer 194 is improved.

Then, the substrate 351 is bonded to a surface of the insulating layer 194 with the adhesive layer 142 (FIG. 6C).

As the adhesive layer 142, any of a variety of curable adhesives such as a reactive curable adhesive, a thermosetting adhesive, an anaerobic adhesive, and a photocurable adhesive such as an ultraviolet curable adhesive can be used. Alternatively, an adhesive sheet or the like may be used.

For the substrate 351, a polyester resin such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), a polyacrylonitrile resin, an acrylic resin, a polyimide resin, a polymethyl methacrylate resin, a polycarbonate (PC) resin, a polyethersulfone (PES) resin, a polyamide resin (e.g., nylon or aramid), a polysiloxane resin, a cycloolefin resin, a polystyrene resin, a polyamide-imide resin, a polyurethane resin, a polyvinyl chloride resin, a polyvinylidene chloride resin, a polypropylene resin, a polytetrafluoroethylene (PTFE) resin, an ABS resin, or cellulose nanofiber can be used, for example. Any of a variety of materials such as glass, quartz, a resin, a metal, an alloy, and a semiconductor can be used for the substrate 351. The substrate 351 formed using any of a variety of materials such as glass, quartz, a resin, a metal, an alloy, and a semiconductor may be thin enough to be flexible.

After that, the formation substrate 350 is peeled (FIG. 7A).

The separation occurs at the interface between the separation layer 311 and the formation substrate 350, so that the separation layer 311 is exposed (FIGS. 7A and 7B).

Note that in the case of employing the step illustrated in FIG. 5B2 instead of the step illustrated in FIG. 5B1, the separation occurs at the interface between the insulating layer 355 and the separation layer 311.

Before the separation, a separation trigger may be formed in the separation layer 311. For example, part of or the entire separation layer 311 may be irradiated with laser light, in which case the separation layer 311 can be embrittled or the adhesion between the separation layer 311 and the formation substrate 350 can be reduced.

The formation substrate 350 can be peeled by applying a perpendicular tensile force to the separation layer 311, for example. Specifically, the formation substrate 350 can be peeled by pulling up the substrate 351 by part of its suction-attached top surface.

The separation trigger may be formed by inserting a sharp instrument such as a knife between the separation layer 311 and the formation substrate 350. Alternatively, the separation trigger may be formed by cutting the separation layer 311 from the substrate 351 side with a sharp instrument.

Next, the separation layer 311 is processed into the electrode 311 a and the conductive layer 311 b (FIG. 7C). The opening 451 overlapping with the light-emitting region and the coloring layer 134 of the light-emitting element 170 is provided in the electrode 311 a. The electrode 311 a and the conductive layer 311 b can be formed in the following manner: a resist mask is formed over the separation layer 311, the separation layer 311 is etched, and the resist mask is removed. The separation layer 311 can be processed by wet etching or dry etching; it is particularly preferable to use dry etching. Note that the conductive layer 311 c illustrated in FIG. 2 can be formed at the same time as the electrode 311 a and the conductive layer 311 b by processing the separation layer 311.

Subsequently, the alignment film 133 a is formed over the electrode 311 a (FIG. 8A). The alignment film 133 a can be formed in the following manner: a thin film is formed using a resin or the like, and then, rubbing treatment is performed.

Then, the substrate 361 obtained through the steps described using FIG. 5A and the substrate 351 obtained through the steps up to the step illustrated in FIG. 8A are bonded to each other with the liquid crystal layer 112 provided therebetween (FIG. 8B). The substrate 351 and the substrate 361 are bonded to each other with the adhesive layer 141. For materials of the adhesive layer 141, the description of the materials that can be used for the adhesive layer 142 can be referred to. Note that in the connection portion 252 illustrated in FIG. 2, the adhesive layer 141 contains a conductive particle. Accordingly, the electrode 113 and the conductive layer 311 c can be electrically connected to each other when the substrate 351 and the substrate 361 are bonded to each other.

In the liquid crystal element 180 illustrated in FIG. 8B, the electrode 311 a part of which functions as the pixel electrode, the liquid crystal layer 112, and the electrode 113 part of which functions as the common electrode are stacked. The liquid crystal element 180 is formed so as to overlap with the coloring layer 131.

Through the above steps, the display device 300 can be fabricated.

Note that the polarizing plate 135 is placed on the outer surface of the substrate 361.

The conductive layer 311 b is electrically connected to the FPC 372 through the connection layer 242. As a result, the FPC 372 and the wiring 365 can be electrically connected to each other.

As described above, in Example 1 of manufacturing method of display device, the surface of the separation layer does not particularly need to be subjected to treatment such as plasma treatment after the formation of the separation layer. Furthermore, a low-cost material can be used for the separation layer and application to large substrates can be easily made. Thus, the display device of this embodiment can be manufactured with high mass productivity at low cost.

In Example 1 of manufacturing method of display device, the electrode of the display element can be formed by processing the separation layer that is exposed by peeling. Since the electrode is formed using the separation layer, the removal of the separation layer is not required. In addition, a conductive film to be the electrode of the display element does not need to be formed in a different step than the separation layer. Accordingly, a manufacturing process can be simplified.

Example 2 of Manufacturing Method of Display Device

Next, a manufacturing method of a display device that is different from that described in Example 1 of manufacturing method of display device will be specifically described.

Example 2 of manufacturing method of display device is different from Example 1 of manufacturing method of display device mainly in that the reflective electrode of the liquid crystal element is formed without using the separation layer 311 and in that the separation layer 311 is removed after peeling.

Note that detailed descriptions of steps similar to those in Example 1 of manufacturing method of display device are sometimes omitted.

First, components from the coloring layer 131 to the alignment film 133 b are formed over the substrate 361 (FIG. 9A). Steps for forming the components are similar to those described with reference to FIG. 5A in Example 1 of manufacturing method of display device.

Note that steps illustrated in FIGS. 9B, 9C1, and 9C2, FIGS. 10A and 10B, FIGS. 11A and 11B, and FIGS. 12A and 12B are performed independently of the steps illustrated in FIG. 9A.

First, the separation layer 311 is formed over the formation substrate 350 (FIG. 9B). In the step illustrated in FIG. 9B, a material is selected that would cause separation at the interface between the formation substrate 350 and the separation layer 311 when the formation substrate 350 is peeled.

Alternatively, as described in Example 1 of manufacturing method of display device with reference to FIG. 5B2, the insulating layer 355 may be formed over the formation substrate 350 and the separation layer 311 may be formed over the insulating layer 355.

Since the reflective electrode of the liquid crystal element is formed without using the separation layer 311 in Example 2 of manufacturing method of display device, the separation layer 311 does not necessarily have reflexibility.

Then, an electrode 111 and a conductive layer 111 c are formed over the separation layer 311 (FIG. 9C1). The electrode 111 has the opening 451 above the separation layer 311. The electrode 111 and the conductive layer 111 c can be formed in the following manner: a conductive film is formed, a resist mask is formed, the conductive film is etched, and the resist mask is removed. The electrode 111 and the conductive layer 111 c are formed using a conductive material that reflects visible light.

Alternatively, an electrode 111 a and the conductive layer 111 c are formed over the separation layer 311, an electrode 111 b is formed over the electrode 111 a, and a conductive layer 111 d is formed over the conductive layer 111 c (FIG. 9C2). The electrode 111 b has the opening 451 above the electrode 111 a. The electrode 111 a and the conductive layer 111 c can be formed in the following manner: a conductive film is formed, a resist mask is formed, the conductive film is etched, and the resist mask is removed. The electrode 111 b and the conductive layer 111 d can be formed in a similar manner. The electrode 111 a and the conductive layer 111 c are formed using a conductive material that transmits visible light. The electrode 111 b and the conductive layer 111 d are formed using a conductive material that reflects visible light.

As illustrated in FIG. 9C2, the electrode 111 a that transmits visible light is preferably provided across the opening 451. Accordingly, liquid crystals are aligned in a region overlapping with the opening 451 as in the other regions, in which case an alignment defect of the liquid crystals is prevented from being generated in a boundary portion of these regions and undesired light leakage can be suppressed.

As described above, the separation layer 311 is removed after the peeling in Example 2 of manufacturing method of display device. Thus, it is preferable that the etching selectivity ratio of the separation layer 311 to the electrode 111 (or the electrode 111 a) in contact with the separation layer 311 be sufficiently large, in which case the electrode 111 (or the electrode 111 a) can be prevented from being removed when the separation layer 311 is removed.

The following description is for the case of employing the step illustrated in FIG. 9C1. Note that the following description can also be applied to the case of employing the step illustrated in FIG. 9C2.

The insulating layer 220 is formed (FIG. 10A). Then, an opening that reaches the electrode 111 is provided in the insulating layer 220.

Next, the connection portion 204, the connection portion 207, the transistor 205, and the transistor 206 are formed over the insulating layer 220.

Specifically, first, the conductive layer 221 a, the conductive layer 221 b, and the conductive layer 221 c are formed over the insulating layer 220. At this time, the conductive layer 221 b and the electrode 111 are connected to each other through the opening in the insulating layer 220 at the connection portion 207, and the conductive layer 221 c and the conductive layer 111 c are connected to each other through the opening in the insulating layer 220 at the connection portion 204.

Subsequently, the insulating layer 211 is formed and the semiconductor layer 231 is formed over the insulating layer 211.

Next, the conductive layers 222 a and 222 b and the wiring 365 are formed. Here, the conductive layer 222 a included in the transistor 206 is electrically connected to the conductive layer 221 b. As a result, the electrode 111 and the conductive layer 222 a can be electrically connected to each other at the connection portion 207. At the connection portion 204, the wiring 365 and the conductive layer 111 c are electrically connected to each other with the conductive layer 221 c provided therebetween.

In the above manner, the transistor 206 can be fabricated (FIG. 10A).

Next, the insulating layer 212 that covers the transistor 206 is formed and the conductive layer 223 is formed over the insulating layer 212, so that the transistor 205 is completed (FIG. 10A).

Then, the insulating layer 213 is formed and the coloring layer 134 is formed over the insulating layer 213 (FIG. 10A). After that, components from the insulating layer 214 to the insulating layer 194 are formed (FIG. 10B). Next, the substrate 351 is bonded to a surface of the insulating layer 194 with the adhesive layer 142 (FIG. 10B). Steps for forming the components are similar to those described with reference to FIG. 5C and FIGS. 6A to 6C in Example 1 of manufacturing method of display device.

After that, the formation substrate 350 is peeled (FIG. 11A).

The separation occurs at the interface between the separation layer 311 and the formation substrate 350, so that the separation layer 311 is exposed (FIGS. 11A and 11B).

Next, the separation layer 311 is removed so that the insulating layer 220, the conductive layer 111 c, and the electrode 111 are exposed (FIG. 12A). The separation layer 311 can be removed by wet etching or dry etching. The use of the condition where the etching selectivity ratio of the separation layer 311 to the electrode 111 and the conductive layer 111 c is large can prevent the electrode 111 and the conductive layer 111 c from being removed.

In the case of using titanium for the separation layer 311, for example, an ammonia hydrogen peroxide mixture (a mixed solution of ammonia, water, and a hydrogen peroxide solution) is preferably used because etching can be performed at room temperature and the etching selectivity ratio to other films can be large.

Subsequently, the alignment film 133 a is formed over the electrode 111 (FIG. 12B). The alignment film 133 a can be formed in the following manner: a thin film is formed using a resin or the like, and then, rubbing treatment is performed.

Then, the substrate 361 obtained from the steps described using FIG. 9A and the substrate 351 obtained from the steps up to the step illustrated in FIG. 12B are bonded to each other with the liquid crystal layer 112 provided therebetween (FIG. 13A). The substrate 351 and the substrate 361 are bonded to each other with the adhesive layer 141.

In the liquid crystal element 180 illustrated in FIG. 13A, the electrode 111 part of which functions as the pixel electrode, the liquid crystal layer 112, and the electrode 113 part of which functions as the common electrode are stacked. The liquid crystal element 180 is formed so as to overlap with the coloring layer 131.

The polarizing plate 135 is placed on the outer surface of the substrate 361. Furthermore, the FPC 372 and the wiring 365 are electrically connected to each other through the connection layer 242.

FIG. 13B is a cross-sectional view of a display device, which is formed in the case of employing the step illustrated in FIG. 9C2. The display device illustrated in FIG. 13B does not include the electrode 111 but the electrode 111 a and the electrode 111 b.

As described above, in Example 2 of manufacturing method of display device, the surface of the separation layer does not particularly need to be subjected to treatment such as plasma treatment after the formation of the separation layer. Furthermore, a low-cost material can be used for the separation layer and application to large substrates can be easily made. Thus, the display device of this embodiment can be manufactured with high mass productivity at low cost.

Structure Example of Transistor

There is no particular limitation on the structure of the transistor included in the display device of one embodiment of the present invention. For example, a planar transistor, a staggered transistor, or an inverted staggered transistor may be used. A top-gate transistor or a bottom-gate transistor may be used. Gate electrodes may be provided above and below a channel.

FIGS. 14A to 14E illustrate structure examples of transistors.

A transistor 110 a illustrated in FIG. 14A is a top-gate transistor.

The transistor 110 a includes a conductive layer 221, the insulating layer 211, the semiconductor layer 231, the insulating layer 212, the conductive layer 222 a, and the conductive layer 222 b. The semiconductor layer 231 is provided over an insulating layer 151. The conductive layer 221 overlaps with the semiconductor layer 231 with the insulating layer 211 positioned therebetween. The conductive layer 222 a and the conductive layer 222 b are electrically connected to the semiconductor layer 231 through openings provided in the insulating layer 211 and the insulating layer 212.

The conductive layer 221 functions as a gate. The insulating layer 211 functions as a gate insulating layer. One of the conductive layer 222 a and the conductive layer 222 b functions as a source and the other functions as a drain.

In the transistor 110 a, the conductive layer 221 can be physically distanced from the conductive layer 222 a or 222 b easily; thus, the parasitic capacitance between the conductive layer 221 and the conductive layer 222 a or 222 b can be reduced.

A transistor 110 b illustrated in FIG. 14B includes, in addition to the components of the transistor 110 a, the conductive layer 223 and an insulating layer 218. The conductive layer 223 is provided over the insulating layer 151. The conductive layer 223 overlaps with the semiconductor layer 231. The insulating layer 218 covers the conductive layer 223 and the insulating layer 151.

The conductive layer 223 functions as one of a pair of gates. Thus, the on-state current of the transistor can be increased and the threshold voltage can be controlled.

FIGS. 14C to 14E each illustrate an example of a stacked-layer structure of two transistors. The structures of the two stacked transistors can be independently determined, and the combination of the structures is not limited to those illustrated in FIGS. 14C to 14E.

FIG. 14C illustrates a stacked-layer structure of a transistor 110 c and a transistor 110 d. The transistor 110 c includes two gates. The transistor 110 d has a bottom-gate structure. Note that the transistor 110 c may have a structure including one gate (top-gate structure). The transistor 110 d may include two gates.

The transistor 110 c includes the conductive layer 223, the insulating layer 218, the semiconductor layer 231, the conductive layer 221, the insulating layer 211, the conductive layer 222 a, and the conductive layer 222 b. The conductive layer 223 is provided over the insulating layer 151. The conductive layer 223 overlaps with the semiconductor layer 231 with the insulating layer 218 positioned therebetween. The insulating layer 218 covers the conductive layer 223 and the insulating layer 151. The conductive layer 221 overlaps with the semiconductor layer 231 with the insulating layer 211 positioned therebetween. Although FIG. 14C illustrates an example where the insulating layer 211 is provided only in a region overlapping with the conductive layer 221, the insulating layer 211 may be provided so as to cover an end portion of the semiconductor layer 231, as illustrated in FIG. 14B and other drawings. The conductive layer 222 a and the conductive layer 222 b are electrically connected to the semiconductor layer 231 through openings provided in the insulating layer 212.

The transistor 110 d includes the conductive layer 222 b, the insulating layer 213, the semiconductor layer 261, the conductive layer 263 a, and the conductive layer 263 b. The conductive layer 222 b includes a region overlapping with the semiconductor layer 261 with the insulating layer 213 positioned therebetween. The insulating layer 213 covers the conductive layer 222 b. The conductive layer 263 a and the conductive layer 263 b are electrically connected to the semiconductor layer 261.

The conductive layer 221 and the conductive layer 223 each function as a gate of the transistor 110 c. The insulating layer 218 and the insulating layer 211 each function as a gate insulating layer of the transistor 110 c. The conductive layer 222 a functions as one of a source and a drain of the transistor 110 c.

The conductive layer 222 b has a portion functioning as the other of the source and the drain of the transistor 110 c and a portion functioning as a gate of the transistor 110 d. The insulating layer 213 functions as a gate insulating layer of the transistor 110 d. One of the conductive layer 263 a and the conductive layer 263 b functions as a source of the transistor 110 d and the other functions as a drain of the transistor 110 d.

The transistor 110 c and the transistor 110 d are preferably applied to a pixel circuit of the light-emitting element 170. For example, the transistor 110 c can be used as a selection transistor and the transistor 110 d can be used as a driving transistor.

The conductive layer 263 b is electrically connected to the electrode 191 that functions as a pixel electrode of the light-emitting element through an opening provided in the insulating layer 217 and the insulating layer 214.

FIG. 14D illustrates a stacked-layer structure of a transistor 110 e and a transistor 110 f. The transistor 110 e has a bottom-gate structure. The transistor 110 f includes two gates. The transistor 110 e may include two gates.

The transistor 110 e includes the conductive layer 221, the insulating layer 211, the semiconductor layer 231, the conductive layer 222 a, and the conductive layer 222 b. The conductive layer 221 is provided over the insulating layer 151. The conductive layer 221 overlaps with the semiconductor layer 231 with the insulating layer 211 positioned therebetween. The insulating layer 211 covers the conductive layer 221 and the insulating layer 151. The conductive layer 222 a and the conductive layer 222 b are electrically connected to the semiconductor layer 231.

The transistor 110 f includes the conductive layer 222 b, the insulating layer 212, the semiconductor layer 261, the conductive layer 223, the insulating layer 218, the insulating layer 213, the conductive layer 263 a, and the conductive layer 263 b. The conductive layer 222 b includes a region overlapping with the semiconductor layer 261 with the insulating layer 212 positioned therebetween. The insulating layer 212 covers the conductive layer 222 b. The conductive layer 263 a and the conductive layer 263 b are electrically connected to the semiconductor layer 261 through openings provided in the insulating layer 213. The conductive layer 223 overlaps with the semiconductor layer 261 with the insulating layer 218 positioned therebetween. The insulating layer 218 is provided in a region overlapping with the conductive layer 223.

The conductive layer 221 functions as a gate of the transistor 110 e. The insulating layer 211 functions as a gate insulating layer of the transistor 110 e. The conductive layer 222 a functions as one of a source and a drain of the transistor 110 e.

The conductive layer 222 b has a portion functioning as the other of the source and the drain of the transistor 110 e and a portion functioning as a gate of the transistor 110 f. The conductive layer 223 functions as another gate of the transistor 110 f. The insulating layer 212 and the insulating layer 218 each function as a gate insulating layer of the transistor 110 f. One of the conductive layer 263 a and the conductive layer 263 b functions as a source of the transistor 110 f and the other functions as a drain of the transistor 110 f.

The conductive layer 263 b is electrically connected to the electrode 191 that functions as a pixel electrode of a light-emitting element through an opening provided in the insulating layer 214.

FIG. 14E illustrates a stacked-layer structure of a transistor 110 g and a transistor 110 h. The transistor 110 g has a top-gate structure. The transistor 110 h includes two gates. The transistor 110 g may include two gates.

The transistor 110 g includes the semiconductor layer 231, the conductive layer 221, the insulating layer 211, the conductive layer 222 a, and the conductive layer 222 b. The semiconductor layer 231 is provided over the insulating layer 151. The conductive layer 221 overlaps with the semiconductor layer 231 with the insulating layer 211 positioned therebetween. The insulating layer 211 overlaps with the conductive layer 221. The conductive layer 222 a and the conductive layer 222 b are electrically connected to the semiconductor layer 231 through openings provided in the insulating layer 212.

The transistor 110 h includes the conductive layer 222 b, the insulating layer 213, the semiconductor layer 261, the conductive layer 223, the insulating layer 218, the insulating layer 217, the conductive layer 263 a, and the conductive layer 263 b. The conductive layer 222 b includes a region overlapping with the semiconductor layer 261 with the insulating layer 213 positioned therebetween. The insulating layer 213 covers the conductive layer 222 b. The conductive layer 263 a and the conductive layer 263 b are electrically connected to the semiconductor layer 261 through openings provided in the insulating layer 217. The conductive layer 223 overlaps with the semiconductor layer 261 with the insulating layer 218 positioned therebetween. The insulating layer 218 is provided in a region overlapping with the conductive layer 223.

The conductive layer 221 functions as a gate of the transistor 110 g. The insulating layer 211 functions as a gate insulating layer of the transistor 110 g. The conductive layer 222 a functions as one of a source and a drain of the transistor 110 g.

The conductive layer 222 b has a portion functioning as the other of the source and the drain of the transistor 110 g and a portion functioning as a gate of the transistor 110 h. The conductive layer 223 functions as another gate of the transistor 110 h. The insulating layer 213 and the insulating layer 218 each function as a gate insulating layer of the transistor 110 h. One of the conductive layer 263 a and the conductive layer 263 b functions as a source of the transistor 110 h and the other functions as a drain of the transistor 110 h.

The conductive layer 263 b is electrically connected to the electrode 191 that functions as a pixel electrode of a light-emitting element through an opening provided in the insulating layer 214.

The display device of this embodiment includes two types of display elements as described above; thus, switching between a plurality of display modes is possible. Accordingly, the display device can have high visibility regardless of the ambient brightness, leading to high convenience.

In any of the manufacturing methods of a display device of this embodiment, the surface of the separation layer does not particularly need to be subjected to treatment such as plasma treatment after the formation of the separation layer. Furthermore, a low-cost material can be used for the separation layer and application to large substrates can be easily made. Thus, the display device of this embodiment can be manufactured with high mass productivity at low cost.

Furthermore, since the electrode of the display element can be formed using the separation layer, the removal of the separation layer is not required. In addition, the electrode of the display element does not need to be formed in a different step than the separation layer. Accordingly, a manufacturing process can be simplified.

This embodiment can be combined with any other embodiment as appropriate. In the case where a plurality of structure examples are described in one embodiment in this specification, some of the structure examples can be combined as appropriate.

Embodiment 2

In this embodiment, more specific structure examples of the display device described in Embodiment 1 will be described with reference to FIGS. 15A, 15B1, 15B2, 15B3, and 15B4, FIG. 16, and FIGS. 17A and 17B.

FIG. 15A is a block diagram of a display device 400. The display device 400 includes the display portion 362, a circuit GD, and a circuit SD. The display portion 362 includes a plurality of pixels 410 arranged in a matrix.

The display device 400 includes a plurality of wirings G1, a plurality of wirings G2, a plurality of wirings ANO, a plurality of wirings CSCOM, a plurality of wirings S1, and a plurality of wirings S2. The plurality of wirings G1, the plurality of wirings G2, the plurality of wirings ANO, and the plurality of wirings CSCOM are each electrically connected to the circuit GD and the plurality of pixels 410 arranged in a direction indicated by an arrow R. The plurality of wirings S1 and the plurality of wirings S2 are each electrically connected to the circuit SD and the plurality of pixels 410 arranged in a direction indicated by an arrow C.

Although the structure including one circuit GD and one circuit SD is illustrated here for simplicity, the circuit GD and the circuit SD for driving liquid crystal elements and the circuit GD and the circuit SD for driving light-emitting elements may be provided separately.

The pixels 410 each include a reflective liquid crystal element and a light-emitting element.

FIGS. 15B1, 15B2, 15B3, and 15B4 illustrate structure examples of the electrode 311 a included in the pixel 410. The electrode 311 a serves as a reflective electrode of the liquid crystal element. The opening 451 is provided in the electrode 311 a in FIGS. 15B1 and 15B2.

In FIGS. 15B1 and 15B2, a light-emitting element 360 positioned in a region overlapping with the electrode 311 a is indicated by a broken line. The light-emitting element 360 overlaps with the opening 451 included in the electrode 311 a. Thus, light from the light-emitting element 360 is emitted to the display surface side through the opening 451.

In FIG. 15B1, the pixels 410 which are adjacent in the direction indicated by the arrow R are pixels emitting light of different colors. As illustrated in FIG. 15B1, the openings 451 are preferably provided in different positions in the electrodes 311 a so as not to be aligned in two adjacent pixels provided in the direction indicated by the arrow R. This allows two light-emitting elements 360 to be apart from each other, thereby preventing light emitted from the light-emitting element 360 from entering a coloring layer in the adjacent pixel 410 (such a phenomenon is referred to as crosstalk). Furthermore, since two adjacent light-emitting elements 360 can be arranged apart from each other, a high-resolution display device is achieved even when EL layers of the light-emitting elements 360 are separately formed with a blocking mask or the like.

In FIG. 15B2, the pixels 410 which are adjacent in a direction indicated by the arrow C are pixels emitting light of different colors. Also in FIG. 15B2, the openings 451 are preferably provided in different positions in the electrodes 311 a so as not to be aligned in two adjacent pixels provided in the direction indicated by the arrow C.

The smaller the ratio of the total area of the opening 451 to the total area except for the opening is, the brighter an image displayed using the liquid crystal element can be. Furthermore, the larger the ratio of the total area of the opening 451 to the total area except for the opening is, the brighter an image displayed using the light-emitting element 360 can be.

The opening 451 may have a polygonal shape, a quadrangular shape, an elliptical shape, a circular shape, a cross-like shape, a stripe shape, a slit-like shape, or a checkered pattern, for example. The opening 451 may be provided close to the adjacent pixel. Preferably, the opening 451 is provided close to another pixel emitting light of the same color, in which case crosstalk can be suppressed.

As illustrated in FIGS. 15B3 and 15B4, a light-emitting region of the light-emitting element 360 may be positioned in a region where the electrode 311 a is not provided, in which case light emitted from the light-emitting element 360 is emitted to the display surface side.

In FIG. 15B3, the light-emitting elements 360 are not aligned in two adjacent pixels 410 provided in the direction indicated by the arrow R. In FIG. 15B4, the light-emitting elements 360 are aligned in two adjacent pixels 410 provided in the direction indicated by the arrow R.

The structure illustrated in FIG. 15B3 can, as mentioned above, prevent crosstalk and increase the resolution because the light-emitting elements 360 included in two adjacent pixels 410 can be apart from each other. The structure illustrated in FIG. 15B4 can prevent light emitted from the light-emitting element 360 from being blocked by the electrode 311 a because the electrode 311 a is not positioned along a side of the light-emitting element 360 which is parallel to the direction indicated by the arrow C. Thus, high viewing angle characteristics can be achieved.

As the circuit GD, any of a variety of sequential circuits such as a shift register can be used. In the circuit GD, a transistor, a capacitor, and the like can be used. A transistor included in the circuit GD can be formed in the same steps as the transistors included in the pixels 410.

The circuit SD is electrically connected to the wirings S1. For example, an integrated circuit can be used as the circuit SD. Specifically, an integrated circuit formed on a silicon substrate can be used as the circuit SD.

For example, a COG method, a COF method, or the like can be used to mount the circuit SD on a pad electrically connected to the pixels 410. Specifically, an anisotropic conductive film can be used to mount an integrated circuit on the pad.

FIG. 16 is an example of a circuit diagram of the pixels 410. FIG. 16 illustrates two adjacent pixels 410.

The pixels 410 each include a switch SW1, a capacitor C1, a liquid crystal element 340, a switch SW2, a transistor M, a capacitor C2, the light-emitting element 360, and the like. The pixel 410 is electrically connected to the wiring G1, the wiring G2, the wiring ANO, the wiring CSCOM, the wiring S1, and the wiring S2. FIG. 16 illustrates a wiring VCOM1 electrically connected to the liquid crystal element 340 and a wiring VCOM2 electrically connected to the light-emitting element 360.

FIG. 16 illustrates an example in which a transistor is used as each of the switches SW1 and SW2.

A gate of the switch SW1 is connected to the wiring G1. One of a source and a drain of the switch SW1 is connected to the wiring S1, and the other is connected to one electrode of the capacitor C1 and one electrode of the liquid crystal element 340. The other electrode of the capacitor C1 is connected to the wiring CSCOM. The other electrode of the liquid crystal element 340 is connected to the wiring VCOM1.

A gate of the switch SW2 is connected to the wiring G2. One of a source and a drain of the switch SW2 is connected to the wiring S2, and the other is connected to one electrode of the capacitor C2 and gates of the transistor M. The other electrode of the capacitor C2 is connected to one of a source and a drain of the transistor M and the wiring ANO. The other of the source and the drain of the transistor M is connected to one electrode of the light-emitting element 360. Furthermore, the other electrode of the light-emitting element 360 is connected to the wiring VCOM2.

FIG. 16 illustrates an example where the transistor M includes two gates between which a semiconductor is provided and which are connected to each other. This structure can increase the amount of current flowing in the transistor M.

The wiring G1 can be supplied with a signal for changing the on/off state of the switch SW1. A predetermined potential can be supplied to the wiring VCOM1. The wiring S1 can be supplied with a signal for changing the orientation of liquid crystals of the liquid crystal element 340. A predetermined potential can be supplied to the wiring CSCOM.

The wiring G2 can be supplied with a signal for changing the on/off state of the switch SW2. The wiring VCOM2 and the wiring ANO can be supplied with potentials having a difference large enough to make the light-emitting element 360 emit light. The wiring S2 can be supplied with a signal for changing the conduction state of the transistor M.

In the pixel 410 of FIG. 16, for example, an image can be displayed in the reflective mode by driving the pixel with the signals supplied to the wiring G1 and the wiring S1 and utilizing the optical modulation of the liquid crystal element 340. In the case where an image is displayed in the transmissive mode, the pixel is driven with the signals supplied to the wiring G2 and the wiring S2 and the light-emitting element 360 emits light. In the case where both modes are performed at the same time, the pixel can be driven with the signals supplied to the wiring G1, the wiring G2, the wiring S1, and the wiring S2.

Although FIG. 16 illustrates an example in which one liquid crystal element 340 and one light-emitting element 360 are provided in one pixel 410, one embodiment of the present invention is not limited thereto. FIG. 17A illustrates an example in which one liquid crystal element 340 and four light-emitting elements 360 (light-emitting elements 360 r, 360 g, 360 b, and 360 w) are provided in one pixel 410. The pixel 410 illustrated in FIG. 17A differs from that in FIG. 16 in being capable of displaying a full-color image with the use of the light-emitting elements by one pixel.

In FIG. 17A, in addition to the wirings in FIG. 16, a wiring G3 and a wiring S3 are connected to the pixel 410.

In the example in FIG. 17A, light-emitting elements emitting red light (R), green light (G), blue light (B), and white light (W) can be used as the four light-emitting elements 360, for example. Furthermore, as the liquid crystal element 340, a reflective liquid crystal element emitting white light can be used. Thus, in the case of displaying an image in the reflective mode, a white image can be displayed with high reflectivity. In the case of displaying an image in the transmissive mode, an image can be displayed with a higher color rendering property at low power consumption.

FIG. 17B illustrates a structure example of the pixel 410 corresponding to FIG. 17A. The pixel 410 includes the light-emitting element 360 w overlapping with the opening included in the electrode 311 a and the light-emitting element 360 r, the light-emitting element 360 g, and the light-emitting element 360 b which are arranged in the periphery of the electrode 311 a. It is preferable that the light-emitting elements 360 r, 360 g, and 360 b have almost the same light-emitting area.

This embodiment can be combined with any other embodiment as appropriate.

Embodiment 3

In this embodiment, described below is the composition of a cloud-aligned composite oxide semiconductor (CAC-OS) applicable to a transistor disclosed in one embodiment of the present invention.

The CAC-OS has, for example, a composition in which elements included in an oxide semiconductor are unevenly distributed. Materials including unevenly distributed elements each have a size of greater than or equal to 0.5 nm and less than or equal to 10 nm, preferably greater than or equal to 1 nm and less than or equal to 2 nm, or a similar size. Note that in the following description of an oxide semiconductor, a state in which one or more metal elements are unevenly distributed and regions including the metal element(s) are mixed is referred to as a mosaic pattern or a patch-like pattern. The region has a size of greater than or equal to 0.5 nm and less than or equal to 10 nm, preferably greater than or equal to 1 nm and less than or equal to 2 nm, or a similar size.

Note that an oxide semiconductor preferably contains at least indium. In particular, indium and zinc are preferably contained. In addition, one or more of, aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, silicon, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, and the like may be contained.

For example, of the CAC-OS, an In—Ga—Zn oxide with the CAC composition (such an In—Ga—Zn oxide may be particularly referred to as CAC-IGZO) has a composition in which materials are separated into indium oxide (InO_(X1), where X1 is a real number greater than 0) or indium zinc oxide (In_(X2)Zn_(Y2)O_(Z2), where X2, Y2, and Z2 are real numbers greater than 0), and gallium oxide (GaO_(X3), where X3 is a real number greater than 0) or gallium zinc oxide (Ga_(X4)Zn_(Y4)O_(Z4), where X4, Y4, and Z4 are real numbers greater than 0), and a mosaic pattern is formed. Then, InO_(X1) or In_(X2)Zn_(Y2)O_(Z2) forming the mosaic pattern is evenly distributed in the film. This composition is also referred to as a cloud-like composition.

That is, the CAC-OS is a composite oxide semiconductor with a composition in which a region including GaO_(X3) as a main component and a region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component are mixed. Note that in this specification, for example, when the atomic ratio of In to an element M in a first region is greater than the atomic ratio of In to an element M in a second region, the first region is described as having higher In concentration than the second region.

Note that a compound including In, Ga, Zn, and O is also known as IGZO. Typical examples of IGZO include a crystalline compound represented by InGaO₃(ZnO)_(m1) (m1 is a natural number) and a crystalline compound represented by In_((1+x0))Ga_((1−x0))O₃(ZnO)_(m0) (−1≤x0≤1; m0 is a given number).

The above crystalline compounds have a single crystal structure, a polycrystalline structure, or a CAAC structure. Note that the CAAC structure is a crystal structure in which a plurality of IGZO nanocrystals have c-axis alignment and are connected in the a-b plane direction without alignment.

The CAC-OS relates to the material composition of an oxide semiconductor. In a material composition of a CAC-OS including In, Ga, Zn, and O, nanoparticle regions including Ga as a main component are observed in part of the CAC-OS and nanoparticle regions including In as a main component are observed in part thereof. These nanoparticle regions are randomly dispersed to form a mosaic pattern. Therefore, the crystal structure is a secondary element for the CAC-OS.

Note that in the CAC-OS, a stacked-layer structure of two or more films with different atomic ratios is not included. For example, a two-layer structure of a film including In as a main component and a film including Ga as a main component is not included.

A boundary between the region including GaO_(X3) as a main component and the region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component is not clearly observed in some cases.

In the case where one or more of aluminum, yttrium, copper, vanadium, beryllium, boron, silicon, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, and the like are contained instead of gallium in a CAC-OS, nanoparticle regions including the selected metal element(s) as a main component(s) are observed in part of the CAC-OS and nanoparticle regions including In as a main component are observed in part thereof, and these nanoparticle regions are randomly dispersed to form a mosaic pattern in the CAC-OS.

The CAC-OS can be formed by a sputtering method under a condition where a substrate is not heated intentionally. In the case where the CAC-OS is formed by a sputtering method, one or more of an inert gas (typically, argon), an oxygen gas, and a nitrogen gas can be used as a deposition gas. Furthermore, the flow rate of the oxygen gas to the total flow rate of the deposition gas in deposition is preferably as low as possible, for example, the flow rate of the oxygen gas is higher than or equal to 0% and lower than 30%, preferably higher than or equal to 0% and lower than or equal to 10%.

The CAC-OS is characterized in that a clear peak is not observed when measurement is conducted using a θ/2θ scan by an out-of-plane method with an X-ray diffraction (XRD). That is, it is found by the XRD that there are no alignment in the a-b plane direction and no alignment in the c-axis direction in the measured areas.

In the CAC-OS, an electron diffraction pattern that is obtained by irradiation with an electron beam with a probe diameter of 1 nm (also referred to as nanobeam electron beam) has regions with high luminance in a ring pattern and a plurality of bright spots appear in the ring-like pattern. Thus, it is found from the electron diffraction pattern that the crystal structure of the CAC-OS includes a nanocrystalline (nc) structure that does not show alignment in the plane direction and the cross-sectional direction.

For example, energy dispersive X-ray spectroscopy (EDX) is used to obtain EDX mapping, and according to the EDX mapping, the CAC-OS of the In—Ga—Zn oxide has a composition in which the regions including GaO_(X3) as a main component and the regions including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component are unevenly distributed and mixed.

The CAC-OS has a structure different from that of an IGZO compound in which metal elements are evenly distributed, and has characteristics different from those of the IGZO compound. That is, in the CAC-OS, regions including GaO_(X3) or the like as a main component and regions including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component are separated to form a mosaic pattern.

The conductivity of a region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component is higher than that of a region including GaO_(X3) or the like as a main component. In other words, when carriers flow through regions including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component, the conductivity of an oxide semiconductor is exhibited. Accordingly, when regions including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component are distributed in an oxide semiconductor like a cloud, high field-effect mobility (μ) can be achieved.

In contrast, the insulating property of a region including GaO_(X3) or the like as a main component is higher than that of a region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component. In other words, when regions including GaO_(X3) or the like as a main component are distributed in an oxide semiconductor, leakage current can be suppressed and favorable switching operation can be achieved.

Accordingly, when a CAC-OS is used for a semiconductor element, the insulating property derived from GaO_(X3) or the like and the conductivity derived from In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) complement each other, whereby high on-state current (I_(on)) and high field-effect mobility (μ) can be achieved.

A semiconductor element including a CAC-OS has high reliability. Thus, the CAC-OS is suitably used in a variety of semiconductor devices typified by a display.

This embodiment can be combined with any other embodiment as appropriate.

Embodiment 4

In this embodiment, a display module and electronic devices of embodiments of the present invention are described.

In a display module 8000 in FIG. 18, a touch panel 8004 connected to an FPC 8003, a display panel 8006 connected to an FPC 8005, a frame 8009, a printed circuit board 8010, and a battery 8011 are provided between an upper cover 8001 and a lower cover 8002.

The display device of one embodiment of the present invention can be used for, for example, the display panel 8006. In that case, a display module with high visibility regardless of the ambient brightness or a display module with low power consumption can be fabricated.

The shape and size of the upper cover 8001 and the lower cover 8002 can be changed as appropriate depending on the sizes of the touch panel 8004 and the display panel 8006.

The touch panel 8004 can be a resistive touch panel or a capacitive touch panel and can be formed to overlap with the display panel 8006. Instead of providing the touch panel 8004, the display panel 8006 can have a touch panel function.

The frame 8009 protects the display panel 8006 and functions as an electromagnetic shield for blocking electromagnetic waves generated by the operation of the printed circuit board 8010. The frame 8009 can also function as a radiator plate.

The printed circuit board 8010 includes a power supply circuit and a signal processing circuit for outputting a video signal and a clock signal. As a power source for supplying power to the power supply circuit, an external commercial power source or the battery 8011 provided separately may be used. The battery 8011 can be omitted in the case of using a commercial power source.

The display module 8000 may be additionally provided with a member such as a polarizing plate, a retardation plate, or a prism sheet.

The display device of one embodiment of the present invention can achieve high visibility regardless of the intensity of external light. Thus, the display device of one embodiment of the present invention can be suitably used for a portable electronic device, a wearable electronic device (wearable device), an e-book reader, or the like.

A portable information terminal 800 illustrated in FIGS. 19A and 19B includes a housing 801, a housing 802, a display portion 803, a display portion 804, a hinge portion 805, and the like.

The housing 801 and the housing 802 are joined together with the hinge portion 805. The portable information terminal 800 can be opened as illustrated in FIG. 19B from a closed state (FIG. 19A).

The display device of one embodiment of the present invention can be used for at least one of the display portion 803 and the display portion 804. In that case, a portable information terminal with high visibility regardless of the ambient brightness or a portable information terminal with low power consumption can be fabricated.

The display portion 803 and the display portion 804 can each display at least one of a text, a still image, a moving image, and the like. When a text is displayed on the display portion, the portable information terminal 800 can be used as an e-book reader.

Since the portable information terminal 800 is foldable, the portable information terminal 800 has high portability and excellent versatility.

A power button, an operation button, an external connection port, a speaker, a microphone, or the like may be provided for the housing 801 and the housing 802.

A portable information terminal 810 illustrated in FIG. 19C includes a housing 811, a display portion 812, an operation button 813, an external connection port 814, a speaker 815, a microphone 816, a camera 817, and the like.

The display device of one embodiment of the present invention can be used for the display portion 812. In that case, a portable information terminal with high visibility regardless of the ambient brightness or a portable information terminal with low power consumption can be fabricated.

The portable information terminal 810 includes a touch sensor in the display portion 812. Operations such as making a call and inputting a character can be performed by touch on the display portion 812 with a finger, a stylus, or the like.

With the operation button 813, the power can be turned on or off. In addition, types of images displayed on the display portion 812 can be switched; for example, switching an image from a mail creation screen to a main menu screen is performed with the operation button 813.

When a detection device such as a gyroscope sensor or an acceleration sensor is provided inside the portable information terminal 810, the direction of display on the screen of the display portion 812 can be automatically changed by determining the orientation of the portable information terminal 810 (whether the portable information terminal 810 is placed horizontally or vertically). Furthermore, the direction of display on the screen can be changed by touch on the display portion 812, operation with the operation button 813, sound input using the microphone 816, or the like.

The portable information terminal 810 functions as, for example, one or more of a telephone set, a notebook, and an information browsing system. Specifically, the portable information terminal 810 can be used as a smartphone. The portable information terminal 810 is capable of executing a variety of applications such as mobile phone calls, e-mailing, viewing and editing texts, music reproduction, reproducing a moving image, Internet communication, and computer games, for example.

A camera 820 illustrated in FIG. 19D includes a housing 821, a display portion 822, operation buttons 823, a shutter button 824, and the like. Furthermore, an attachable lens 826 is attached to the camera 820.

The display device of one embodiment of the present invention can be used for the display portion 822. The use of the display portion with high visibility regardless of the ambient brightness can increase the convenience of the camera. Furthermore, a camera with low power consumption can be fabricated.

Although the lens 826 of the camera 820 here is detachable from the housing 821 for replacement, the lens 826 may be incorporated into the housing 821.

A still image or a moving image can be taken with the camera 820 at the press of the shutter button 824. In addition, images can also be taken by the touch of the display portion 822 which serves as a touch panel.

Note that a stroboscope, a viewfinder, or the like can be additionally attached to the camera 820. Alternatively, these may be incorporated into the housing 821.

FIGS. 20A to 20E illustrate electronic devices. These electronic devices each include a housing 9000, a display portion 9001, a speaker 9003, an operation key 9005 (including a power switch or an operation switch), a connection terminal 9006, a sensor 9007 (a sensor having a function of measuring force, displacement, position, speed, acceleration, angular velocity, rotational frequency, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, oscillation, odor, or infrared rays), a microphone 9008, and the like.

The display device of one embodiment of the present invention can be suitably used for the display portion 9001. Thus, an electronic device including a display portion with high visibility regardless of the surrounding brightness can be manufactured. Furthermore, an electronic device with low power consumption can be fabricated.

The electronic devices illustrated in FIGS. 20A to 20E can have a variety of functions, for example, a function of displaying a variety of information (a still image, a moving image, a text image, and the like) on the display portion, a touch panel function, a function of displaying a calendar, the date, the time, and the like, a function of controlling processing with a variety of software (programs), a wireless communication function, a function of being connected to a variety of computer networks with a wireless communication function, a function of transmitting and receiving a variety of data with a wireless communication function, a function of reading a program or data stored in a storage medium and displaying the program or data on the display portion, and the like. Note that the functions of the electronic devices illustrated in FIGS. 20A to 20E are not limited to the above, and the electronic devices may have other functions.

FIG. 20A is a perspective view of a watch-type portable information terminal 9200. FIG. 20B is a perspective view of a watch-type portable information terminal 9201.

The portable information terminal 9200 illustrated in FIG. 20A is capable of executing a variety of applications such as mobile phone calls, e-mailing, viewing and editing texts, music reproduction, Internet communication, and computer games. The display surface of the display portion 9001 is bent, and an image can be displayed on the bent display surface. The portable information terminal 9200 can employ near field communication conformable to a communication standard. In that case, for example, mutual communication between the portable information terminal 9200 and a headset capable of wireless communication can be performed, and thus hands-free calling is possible. The portable information terminal 9200 includes the connection terminal 9006, and data can be directly transmitted to and received from another information terminal via a connector. Power charging through the connection terminal 9006 is also possible. Note that the charging operation may be performed by wireless power feeding without using the connection terminal 9006.

Unlike in the portable information terminal illustrated in FIG. 20A, the display surface of the display portion 9001 is not curved in the portable information terminal 9201 illustrated in FIG. 20B. Furthermore, the external state of the display portion of the portable information terminal 9201 is a non-rectangular shape (a circular shape in FIG. 20B).

FIGS. 20C to 20E are perspective views of a foldable portable information terminal 9202. FIG. 20C is a perspective view illustrating the portable information terminal 9202 that is opened. FIG. 20D is a perspective view illustrating the portable information terminal 9202 that is being opened or being folded. FIG. 20E is a perspective view illustrating the portable information terminal 9202 that is folded.

The folded portable information terminal 9202 is highly portable, and the opened portable information terminal 9202 is highly browsable due to a seamless large display region. The display portion 9001 of the portable information terminal 9202 is supported by three housings 9000 joined together by hinges 9055. By folding the portable information terminal 9202 at a connection portion between two housings 9000 with the hinges 9055, the portable information terminal 9202 can be reversibly changed in shape from opened to folded. For example, the portable information terminal 9202 can be bent with a radius of curvature of greater than or equal to 1 mm and less than or equal to 150 mm.

This embodiment can be combined with any other embodiment as appropriate.

This application is based on Japanese Patent Application serial No. 2016-140282 filed with Japan Patent Office on Jul. 15, 2016, the entire contents of which are hereby incorporated by reference. 

What is claimed is:
 1. A display device comprising: a first display element; a second display element; an insulating layer; a first transistor; and a second transistor, wherein the first display element comprises a first pixel electrode configured to reflect visible light and a liquid crystal layer, wherein the second display element is configured to emit visible light, wherein the second display element comprises a second pixel electrode and a common electrode, wherein the first pixel electrode is on an opposite side of the insulating layer from the second pixel electrode, wherein the liquid crystal layer is on an opposite side of the first pixel electrode from the insulating layer, wherein the common electrode is on an opposite side of the second pixel electrode from the insulating layer, wherein the liquid crystal layer comprises a first region overlapping with the first pixel electrode and a second region overlapping with the second display element, wherein a thickness of the liquid crystal layer in the first region is smaller than a thickness of the liquid crystal layer in the second region, wherein the first transistor is configured to control driving of the first display element, wherein the second transistor is configured to control driving of the second display element, and wherein the insulating layer comprises a portion serving as a gate insulating layer of the first transistor and a portion serving as a gate insulating layer of the second transistor.
 2. The display device according to claim 1, wherein the first pixel electrode comprises an opening portion, wherein the second display element comprises a region overlapping with the opening portion, and wherein the second display element is configured to emit visible light toward the opening portion.
 3. A display device comprising: a first display element; a second display element; a first insulating layer; a second insulating layer; a first transistor; and a second transistor, wherein the first transistor is configured to control driving of the first display element, wherein the second transistor is configured to control driving of the second display element, wherein the first display element comprises a first pixel electrode configured to reflect visible light and a liquid crystal layer, wherein the second display element is configured to emit visible light, wherein the second display element comprises a second pixel electrode and a common electrode, wherein the first transistor and the second transistor are between the first insulating layer and the second insulating layer, wherein the first transistor is electrically connected to the first pixel electrode through an opening in the first insulating layer, wherein the second transistor is electrically connected to the second pixel electrode through an opening in the second insulating layer, wherein the liquid crystal layer is on an opposite side of the first pixel electrode from the first insulating layer, wherein the common electrode is on an opposite side of the second pixel electrode from the second insulating layer, wherein the liquid crystal layer comprises a first region overlapping with the first pixel electrode and a second region overlapping with the second display element, and wherein a thickness of the liquid crystal layer in the first region is smaller than a thickness of the liquid crystal layer in the second region.
 4. The display device according to claim 3, wherein one or both of the first transistor and the second transistor comprises an oxide semiconductor in a channel formation region.
 5. The display device according to claim 3, wherein the first pixel electrode comprises an opening portion, wherein the second display element comprises a region overlapping with the opening portion, and wherein the second display element is configured to emit visible light toward the opening portion.
 6. A display module comprising: the display device according to claim 3; and a circuit board.
 7. An electronic device comprising: the display module according to claim 6; and at least one of an antenna, a battery, a housing, a camera, a speaker, a microphone, and an operation button.
 8. A method for manufacturing a display device comprising: forming a first common electrode over a first substrate; forming a separation layer configured to reflect visible light over a formation substrate; forming an insulating layer over the separation layer; forming a second display element comprising a second pixel electrode configured to transmit visible light, a light-emitting layer, and a second common electrode configured to reflect visible light over the insulating layer; bonding the formation substrate and a second substrate to each other with the second display element interposed between the formation substrate and the second substrate; separating the formation substrate and the separation layer from each other; forming a first pixel electrode by processing the separation layer after the step of separating; and bonding the first substrate and the second substrate to each other with an adhesive with a liquid crystal layer interposed between the first common electrode and the first pixel electrode, wherein a first display element comprises the first pixel electrode configured to reflect visible light, the liquid crystal layer, and the first common electrode configured to transmit visible light.
 9. The method for manufacturing a display device, according to claim 8, wherein the separation layer is processed into the first pixel electrode having an opening in a region overlapping with the second display element.
 10. The method for manufacturing a display device, according to claim 8, wherein the adhesive used for bonding the first substrate and the second substrate comprises a conductive particle, wherein the separation layer is processed into the first pixel electrode and a conductive layer in the step of forming the first pixel electrode, and wherein the first common electrode and the conductive layer are electrically connected to each other via the conductive particle in the step of bonding the first substrate and the second substrate.
 11. The manufacturing method of a display device, according to claim 8, wherein a nickel film is formed as the separation layer in contact with the formation substrate, and wherein a maximum temperature applied to the separation layer in a period from forming the separation layer until separating the formation substrate and the separation layer from each other is higher than 150° C. and lower than 450° C.
 12. The manufacturing method of a display device, according to claim 8, wherein a first insulating layer comprising nitrogen and silicon is formed over the formation substrate, wherein a second insulating layer comprising oxygen and silicon is formed over the first insulating layer, wherein a third insulating layer comprising oxygen, fluorine, and silicon is formed over the second insulating layer, and wherein a titanium film is formed as the separation layer over the third insulating layer.
 13. A method for manufacturing a display device comprising: forming a first common electrode over a first substrate; forming a separation layer over a formation substrate; forming a first pixel electrode over the separation layer; forming an insulating layer over the first pixel electrode; forming a second display element comprising a second pixel electrode configured to transmit visible light, a light-emitting layer, and a second common electrode configured to reflect visible light over the insulating layer; bonding the formation substrate and a second substrate to each other with the second display element interposed between the formation substrate and the second substrate; separating the formation substrate and the separation layer from each other; removing the separation layer to expose the first pixel electrode after the step of separating; and bonding the first substrate and the second substrate to each other with an adhesive with a liquid crystal layer interposed between the first common electrode and the first pixel electrode, wherein a first display element comprises the first pixel electrode configured to reflect visible light, the liquid crystal layer, and the first common electrode configured to transmit visible light.
 14. The method for manufacturing a display device according to claim 13, further comprising the steps of: providing an opening in the first pixel electrode after the first pixel electrode is formed; and forming the second display element in a region overlapping with the opening.
 15. The manufacturing method of a display device, according to claim 13, wherein the adhesive used for bonding the first substrate and the second substrate comprises a conductive particle, wherein the first pixel electrode and a conductive layer are formed by processing a conductive film in the step of forming the first pixel electrode, and wherein the first common electrode and the conductive layer are electrically connected to each other via the conductive particle in the step of bonding the first substrate and the second substrate.
 16. The manufacturing method of a display device, according to claim 13, wherein a nickel film is formed as the separation layer in contact with the formation substrate, and wherein a maximum temperature applied to the separation layer in a period from forming the separation layer until separating the formation substrate and the separation layer from each other is higher than 150° C. and lower than 450° C.
 17. The manufacturing method of a display device, according to claim 13, wherein a first insulating layer comprising nitrogen and silicon is formed over the formation substrate, wherein a second insulating layer comprising oxygen and silicon is formed over the first insulating layer, wherein a third insulating layer comprising oxygen, fluorine, and silicon is formed over the second insulating layer, and wherein a titanium film is formed as the separation layer over the third insulating layer. 